A confusing array of names is given to clocks. We have described the most common varieties.
Wall clock is a generic term for types of clock that must be hung on a wall.
Included in this broad category are lantern and Act of Parliament clocks. Some smaller regulator clocks are also wall clocks.
The term 'table clock' is a generic name for clocks placed on a table, mantel or other horizontal surface except the floor
Included in this main category are:
The style of clock called a 'lantern clock' was the first type of domestic clock.
A lantern clock is square-ish, and is a wall clock, being hung from a hook on the wall. The distinguishing features are a bell on top of the clock, and a metal case. The bell is struck to indicate the hours. Most original lantern clocks have an hour hand only.
These clocks were made of iron originally but later brass was preferred, often with thickly gilded dials. The earliest would run for just 12 hours, needing adjustment every day. Later models ran for one day or perhaps 30 hours.
The weights hang down below. They have no pendulum, which was not invented until 1658. Originally, lantern clocks had a balance wheel escapement but these rarely survive. Many were converted in the late 17th century to short pendulum and verge escapements, and later to a long pendulum with an anchor escapement.
They date from the 1620s at the earliest and were built throughout the 17th and 18th centuries. Reproductions have continued to be made.
These can also be called chamber or bird-cage clocks.
The style of table clock called a 'bracket clock' evolved from the lantern clock.
When lantern clocks were given wooden cases and mounted on a wooden bracket, this gave rise to the term 'bracket' clock.
Early bracket clocks were wall-mounted and weight-driven but later models are spring-driven and are therefore table clocks.
Bracket clocks are distinguished by having a handle on the top and they are taller and narrower than a mantel clock.
From about 1750, London makers concentrated on bracket clocks; most longcase clocks after this date were made elsewhere.
‘Regulator’ is a general term used for a clock against which other clocks were regulated. It came to mean an accurate clock.
A true regulator would not have striking work or chiming, because a certain amount of interference between the going of the clock and the striking or chiming would interfere with the time keeping. Every effort went into the timekeeping element of the clock, and all unnecessary interferences were eliminated.
Regulators can take almost any form. They are sometimes Longcases, but more often are Vienna regulators.
Vienna regulators. In the 19th Century it became increasingly necessary for railway offices and commercial offices to have a good timekeeper. Vienna regulators were made in large numbers to satisfy this demand. Where a Vienna has a seconds hand it often completes a revolution in 45 seconds; it is only there to indicate the clock is running.
A watchmaker’s regulator is another type of regulator. It was used by watch and clockmakers and is quite unlike any domestic clock. The only feature it shares with the Vienna regulator is the deadbeat escapement. Otherwise, it has:
The timekeeping of a Vienna is typically about five seconds a day whereas the timekeeping of a watchmakers regulator would be nearer a few seconds a month.The regulator clock was designed for maximum accuracy and generally had very restrained decoration. It had a modified form of the anchor escapement called the 'dead beat' escapement. From about 1810, they often had a glass door.
The 'Act of Parliament clock' or 'Tavern Clock' appeared in the early decades of the 18th century. They became more common when King George III introduced a government tax on all clocks and watches in 1779. This made timepieces very expensive, so people relied more and more on clocks in public places. There were large clocks on churches and public buildings, but a smaller design of clock was needed for smaller buildings such as taverns.
Originally, the faces of these clocks were in a dark wood or painted. This evolved by the early 19th century into the English Dial Clock, with a round white dial and brass bezel.
The 'dial clock' is a minimalist wall clock; it is simply a clock face with a movement in a simple case placed behind. They appeared in the early 1800s and were made throughout the 19th century. The English style of Dial Clock has a white face and brass bezel.
The mantel clock is a spring-driven table clock intended for placing on the mantel over a fireplace.
Technically, it is like a bracket clock but has no handle and is often low and wide. Another pattern was a balloon shape, with a large face, a pinched waist, and flaring out to the base. Generally they are more ornate than a bracket clock. This is true even for English ones; for example English mantel clocks from the mid-19th century may have significant gilding.
French Victorian mantel clocks often had garnitures; these are separate but related decorative pieces such as figurines or candlesticks placed either side of the clock. This fashion continued into the early 20th century.
The style of clock known as a 'Pendule de Voyage', or 'carriage clock' is a table clock, usually metal-cased, and intended for travelling. It is therefore small and may perhaps have a protective case. This style is a clock that will go well in the smaller rooms of your period home.
The first carriage clock was made very early in the 19th Century by Abraham Louis Breguet. By 1810, the basic design of the carriage clock was much as we know it now. Breguet's carriage clock cases were either wooden in the empire style, metal in the empire style or hump-backed silver cases.
However, the first production carriage clocks appeared in Paris in 1830 made by Paul Garnier. He invented the 'chaff cutter' escapement.
Carriage clocks not only tell the time on a journey, but also strike the hours and often have an alarm. This makes them very useful, versatile clocks. Other features include 'repeating work', where the last hour struck can be sounded again at will. Striking complications extend to 'Petit Sonnerie' and 'Grand Sonnerie'. Grand Sonnerie is where the previous hour is struck along with the relevant quarter. So from 4.45pm to 5pm it will sound five blows followed by three ting tangs. Petit Sonnerie strikes the hours on the hour but only the quarters at each quarter. If you find a clock described as Grand Sonnerie, but the striking runs down after four days or so, it is only Petit Sonnerie with a component removed to make it strike as a Grand Sonnerie.
Carriage clock escapements are typically English lever, sometimes called 'ratchet tooth' escapements or 'cylinder' escapements. More modern ones have a 'Swiss Club tooth' lever. These are often fitted to old clocks as well, because of the failure of the clock maker to repair them or for economic reasons. Lepine used the duplex escapement, because in France it was thought to be superior.
A pendulum clock uses a pendulum as its time base. From their invention, in 1656, until the 1930s, clocks using pendulum movements were the most accurate. Because of their need to be stationary and immovable while operating, pendulum clocks cannot operate in vehicles; the motion and accelerations of the vehicle will affect the motion and pace of the pendulum, causing inaccuracies.
The pendulum clock was invented by Christiaan Huygens in 1656, based on the pendulum introduced by Galileo Galilei.
Pendulum clocks remained the mechanism of choice for accurate timekeeping for centuries, ending with the Shortt free pendulum observatory clocks invented in 1921 and the pendulum clock of Edward Hall that marked the end of the pendulum era as the most reliable time standard.
Pendulum clocks remain popular for domestic use.
Pendulum clocks typically have four parts:
The pendulum swings with a designed period that varies with the square root of its effective length.
To keep time accurately, pendulums are usually made to not vary in length as the temperature changes. Owing to the expansion of metal, the length of a simple pendulum will vary with temperature, slowing the clock as the temperature rises. Early high-precision clocks used the liquid metal mercury to lift a portion of the pendulum mass in compensation for the increased length of the suspension. John Harrison invented the gridiron pendulum, which uses a sliding "banjo" of solid metals with differing thermal expansion rates such as brass or zinc and steel to achieve a zero-expansion pendulum while avoiding the use of toxic mercury.
By the end of the nineteenth century, materials were available that had a very low inherent change of length with temperature and these were used to make a simple pendulum rod. These included Invar, a nickel/iron alloy; and fused silica, a glass. The latter is still used for pendulums in gravimeters.
The viscosity of the air through which the pendulum swings will vary with atomspheric pressure, humidity, and temperature. This drag also requires power that could otherwise be applied to extending the time between windings. Pendulums are sometimes polished and streamlined to reduce the effects of air drag (which is where most of the driving power goes) on the clock's accuracy. In the late 19th century and early 20th century, pendulums for clocks in astronomical observatories were often operated in a chamber that had been pumped to a low pressure to reduce drag and make the pendulum's operation even more accurate.
As a pendulum clock is necessarily stationary, the clock will be adjusted for local gravity. Since an increased gravity will increase the pendulum speed a pendulum clock not adjusted after movement may be used a gravimeter when small time differences between this and other types of clocks (or a clock at a fixed location) are measured. Other modern forms of gravimeters measure gravity by accurately timing the free fall of a proof mass.
This pendulum is a wheel-like mass (most often four spheres on cross spokes) suspended from a vertical strip (ribbon) of spring steel. Rotation of the mass winds and unwinds the suspension spring, with the energy impulse applied to the top of the spring. As the period of a cycle is quite slow compared to the gravity swing pendulum, it is possible to make clocks that need to be wound only every 30 days, or even only once a year. A clock requiring only annual winding is sometimes called a "400-Day clock", "perpetual clock" or "anniversary clock", the latter sometimes given as a wedding memorialisation gift. Schatz and Kundo, both German firms, were once the main manufacturers of this type of clock. This type is independent of the local force of gravity and is less affected by temperature changes than is an uncompensated pendulum.
The escapement drives the pendulum, usually from a gear train, and is the part that ticks. Most escapements have a locking state and a drive state. In the locking state, nothing moves. The motion of the pendulum switches the escapement to drive, and the escapement then pushes on the pendulum for some part of the pendulum's cycle. A notable but rare exception is Harrison's grasshopper escapement. In precision clocks, the escapement is often driven directly by a small weight or spring that is re-set at frequent intervals by an independent mechanism called a remontoire. This frees the escapement from the effects of variations in the gear train. In the late 19th century, electromechanical escapements were developed. In these, a mechanical switch or a phototube turned an electromagnet on for a brief section of the pendulum's swing. These were used on some of the most precise clocks known. They were usually employed with vacuum pendulums on astronomical clocks. The pulse of electricity that drove the pendulum would also drive a plunger to move the gear train.
In the 20th century, W.H. Shortt invented a free pendulum clock with an accuracy of one-hundredth of a second per day. In this system, the timekeeping pendulum does no work and is kept swinging by a push from a weighted arm (gravity arm) that is lowered onto the pendulum by another (slave) clock just before it is needed. The gravity arm then pushes on the free pendulum, which releases it to drop out of engagement at a time that is set entirely by the free pendulum. Once the gravity arm is released, it trips a mechanism to reset itself ready for release by the slave clock. The whole cycle is kept synchronised by a small blade spring on the pendulum of the slave clock. The slave clock is set to run slightly slow, and the reset circuit for the gravity arm activates a pivoted arm that just engages with the tip of the blade spring. If the slave clock has lost too much time, its blade spring pushes against the arm and this accelerates the pendulum. The amount of this gain is such that the blade spring doesn't engage on the next cycle but does on the next again. This form of clock became the standard for use in observatories from the mid-1920s until superseded by quartz technology.
The 'movement' is simply the mechanism of the clock.
It consists of:
Most clocks have a plated movement; the mechanism is set between two vertical plates at the front and back. In some clocks, such as lantern clocks, the movement is 'posted' - two horizontal frames or plates are separated by four vertical posts. This is also called a 'bedpost' or 'birdcage' movement.
There are three typical power sources used in clocks:
Original lantern, longcase and other wall clocks were weight-driven, whereas bracket, carriage, mantel, skeleton, novelty and some wall clocks used a spring. Electric clocks began to appear in the late Victorian period, but mainly date from the 20th century.
In a mechanical clock, the regulator is called an 'escapement'; it controls the 'escape' of power from the spring or weight.
The first common escapement was the 'verge'. This consists of a crown wheel (a wheel with inclined teeth) and a wheel-topped piece (the verge). Pegs ('palletts') on the verge are pushed by the teeth of the crown, oscillating the balance wheel. It remained in use until about 1800. A variation of this was the foliot; a bar with adjustable weights replaced the balance wheel.
Clocks using this type of escapement have to be exactly level otherwise the balance wheel or foliot will rotate unevenly.
The anchor escapement of 1670 is controlled by the swing of the pendulum. The anchor is a C-shaped piece of metal on the ends of which are the teeth which perform the same function as the palletts on the verge. These control the movement of the escape wheel which is like a flattened crown wheel. Many verge clocks were converted to use the anchor escapement.
A third type of escapement is the 'dead beat' escapement; this is much more rare and used mainly on regulators and other precision clocks.
In a longcase clock, the escapement is usually of one of two types - anchor and dead beat. Anchor escapements are typical from the late 17th century to the middle of the 19th.
In a bracket clock, the escapement was usually a verge in the 17th and 18th centuries, but some in the late 18th century used a short pendulum with an anchor escapement.
In the 18th century, the fusee was introduced in spring movements; this uses a conical spool and a wire to even out the pull of the spring.
In a clock, the escapement delivers an even source of power to the train. This is the set of cog wheels which drives the hands and striking.
By adding wheels of different sizes and patterns of notches or pins to the train, the gearing can be used to rotate hands at different speeds and to strike hours and quarters.
The striking in a clock is an extra part of the movement which operates bells or chimes.
If only the hour is struck, one extra weight or spring is required, with one extra winding hole. If the half and quarter hours are also struck, a second additional weight or spring is added, with a third winding hole.
The most popular chime, now known as the 'Westminster chime', is evolved from a phrase from the fifth bar of Handel's Messiah, 'I know that my redeemer liveth'. In about 1793, Revd Dr Joseph Jowett, Regius Professor of Civil Law at Cambridge University, is said to have consulted with Dr Randall, the Professor of Music, or from an undergraduate pupil, William Crotch, and between them they selected and evolved the chime used at Great St Mary's Church, Cambridge.
The tune was then adopted by Lord Grimthorpe, the designer of Big Ben. He remarked that it was strange that so many young men had listened to the chimes while at university but no attempt had been made to produce them elsewhere. The chime is known at Cambridge as 'Jowett's Jig'.
The major components of a clock dial or face are:
Engraved metal was the preferred material from the 18th century. Such dials were often decorated with applied spandrels and a separate chapter ring.
Painted metal dials were often of tin. Being relatively cheap, they are typical of provincial clocks. These dials were popular between about 1780 and the early decades of the 19th century, largely replacing engraved metal.
An alternative to paint was enamel.
The chapter ring carries the numerals and minute markings. Engraved chapter rings are normally silvered.
Calendar rings show the date through an aperture.
The earliest hands on lantern clocks took the form of an arrowhead, with an oval centre or boss, and a long tail. The ears of the arrowhead evolved into loops, the boss became round and the tail shortened.
These are decorative elements at the corners of the face. Cherubs are a typical motif.
Early clocks tended to be of iron, but most clockmakers went on to use brass.
The woods used for the case are typically oak, walnut or mahogany. Alternatively, a fruitwood or rosewood may be used.
Other case materials are marble, slate, ebony or ebonised wood.
Decoration may use brass inlay, marquetry, gilt metal, or ormolu. Either the dial or case, or both, may be painted.
From the mid 17th century, most British clocks made significant use of wood in the case. They are usually relatively plain.
Continental clocks make much less use of wood than British clocks. Instead they are often of porcelain, marble, ormolu, or alabaster, heavily decorated with gilt. They tend to be much more ornate.
A timepiece has one winding hole
A half-hour striking clock has two winding holes, as do ting-tang, or bim-bam, quarter hour striking clocks.
A quarter hour chiming, i.e. musical such as Westminster, St. Michael, Whittington etc, clock generally has three winding holes.
Alarm clocks may have one or two winders.
Winding Key Wind Movements:
Most clocks which are wound from the front, wind in a clockwise direction but there are many exceptions; for example, American striking clocks generally wind inwards to the centre of the dial.
Clocks which are wound from the back usually wind in an anticlockwise direction, but again, there are exceptions.
When in doubt, try winding the clock in both directions without using much force. If the key moves in one direction then that is the correct direction for winding. If it does not move in either direction then it is fully wound and there will be another reason for it not going.
Many French clocks have round movements which are clamped in position in the case by two screws at the back. This is not always a secure fixing and, when being wound, the movement can turn in the case putting the clock out of beat (see the page on setting up). To prevent this from happening, hold the bezel (the rim surrounding the dial) while winding.
Always use a well-fitting key and do not let it slip while winding as this can do extensive damage to the movement.
A longcase clock, also tall-case clock, grandfather clocks or floor clocks, are freestanding, weight-driven, pendulum clocks with the pendulum held inside the tower, or waist of the case. Clocks of this style are commonly around 1.8-2.4m (6-8 feet) tall. The case often features elaborately carved ornamentation on the hood, or bonnet, which surrounds and frames the dial, or clock face. The English clockmaker William Clement is credited with the development of this form in 1670. Most longcase clocks are striking clocks, which means they sound the time on each hour or fraction of an hour.
The terms "grandfather", "grandmother", and "granddaughter" have been applied to longcase clocks. Although there is no specifically defined difference among these terms, the general perception seems to be that a clock smaller than 1.5m (5 feet) is a granddaughter; over 1.5m (5 feet) is a grandmother; and over 1.8m (6 feet) is a grandfather.
Traditionally, such clocks were made with two types of movement: eight-day movements and 30-hour movements. A clock with an eight-day movement required winding only once a week, while the generally lower-priced 30-hour clock had to be wound every day. Eight-day clocks are often driven by two weights - one driving the pendulum and the other the striking mechansim, which usually consisted of a bell or chimes. Such movements usually have two keyholes on either side of the dial to wind each one. By contrast, 30-hour clocks often had a single weight to drive both the pendulum and the chimes. Some 30-hour clocks were made with false keyholes, for customers who wished that guests to their home would think that the household was able to afford the more expensive eight-day clock.
Carriage clock is a small, spring-driven clock, designed for travelling, developed in the early 19th century in France. The case, usually plain or gilt-brass, is rectangular with a carrying handle and often set with glass or more rarely enamel or porcelain panels. A feature of carriage clocks is the platform escapement, sometimes visible through a glazed aperture on the top of the case.
A cuckoo clock is a clock, typically pendulum driven, that strikes the hours using small bellows and pipes that imitate the call of the Common Cuckoo in addition to striking a wire gong. The mechanism to produce the cuckoo call was installed in almost every kind of cuckoo clock since the middle of the eighteenth century and has remained almost without variation until the present.
The design of a cuckoo clock is now conventional. Most are made in the traditional style or chalet to hang on a wall. The wooden case is frequently decorated with carved leaves and animals. Most now have an automaton of the bird that appears through a small trap door while the clock is striking.
The bird is often made to move while the clock strikes, typically by means of an arm that lifts the back of the carving. There are two kind of movement: a one-day movement and an eight-day movement. Some have musical movements, and play a tune on a Swiss music box after striking the hours and/or half-hours. Musical cuckoo clocks frequently have other automatisms which move when the music box plays. Cuckoo clocks are almost always weight driven; a very few are spring driven. The weights are made of cast iron in a pine cone shape.
In recent years, quartz battery-powered cuckoo clocks have been available. These do not have genuine cuckoo bellows. The cuckoo bird flaps its wings as it calls to the sound of running water in the background. The call is an actual recording of a cuckoo in the wild. During the cuckoo call the double doors open and the cuckoo emerges only at full hour, and they do not have a gong wire. One thing that is unique about the quartz cuckoos is that it has a light sensor, so when you turn your lights off at night, it automatically turns off the cuckoo call. The weights are conventionally cast in the shape of pine cones made of plastic, as well as the cuckoo bird and hands. The pendulum bob is often another carved leaf. The dial is small, and typically marked with Roman numerals.
The First Cuckoo Clocks
In 1629, many decades before clockmaking was established in the Black Forest, an Augsburg nobleman by the name of Philipp Hainhofer (1578-1647) penned the first known description of a cuckoo clock. The clock belonged to Prince Elector August von Sachsen.
In a widely known handbook on music Musurgia Universalis (1650), the scholar Athanasius Kircher describes a mechanical organ with several automated figures, including a mechanical cuckoo. This book contains the first documented description -in words and pictures- of how a mechanical cuckoo works. The bird automatically opens its beak and moves both its wings and tail. Simultaneously, we hear the call of the cuckoo, created by two organ pipes, tuned to a minor or major third.
In 1669 Domenico Martinelli, in his Handbook on elementary clocks Horologi Elementari (1669), suggests using the call of the cuckoo to indicate the hours. Starting at that time the mechanism of the cuckoo clock was known. Any mechanic or clockmaker, who could read Latin or Italian, knew after reading the books that it was quite doable to have the cuckoo announce the hours.
Subsequently, cuckoo clocks appeared in regions that had not been known for their clockmaking.
A few decades later, people in the Black Forest started to build cuckoo clocks.
The first cuckoo clocks made in the Black Forest
It is not clear who built the first cuckoo clocks in the Black Forest but there is unanimity that the unusual clock with the bird call very quickly conquered the Black Forest. The first Black Forest cuckoo clocks were made in the middle of the 18th century. They had hand-painted shields and wooden clockworks.
There are two main fables from the eighteenth and nineteenth centuries which tell conflicting stories about the origin of the cuckoo clock:
The first is from Father Franz Steyrer, written in 1796. He describes a meeting between two clock traders from Furtwangen (Black Forest) who met a travelling Bohemian trader who sold wooden cuckoo clocks. Both the Furtwangen traders were so excited that they bought one. On bringing it home they copied it and showed their imitation to other Black Forest clock traders. Its popularity grew in the region and more and more clockmakers started producing them. The second story is related by another priest, Markus Fidelis Jäck, in a passage from his report "Darstellungen aus der Industrie und des Verkehrs aus dem Schwarzwald" ("Description of Industry and Commerce of the Black Forest"), 1810: "The cuckoo clock was invented (in 1730) by a clock-master from Schönwald (Black Forest). This craftsman adorned a clock with a moving bird that announced the hour with the cuckoo-call. The clock-master got the idea of how to make the cuckoo-call from the bellows of a church organ". As time went on, the second version became the more popular, and is the one generally related today. Unfortunately, neither Steyrer nor Jäck quote any sources for their claims, making them unverifiable.
On the other hand R. Dorer pointed out, in 1948, that Franz Anton Ketterer (1734 - 1806) could not have been the inventor of the cuckoo clock in 1730 because he hadn't then been born. Gerd Bender in "Die Uhrenmacher des hohen Schwarzwaldes und ihre Werke" wrote that the cuckoo clock was not native to the Black Forest. Schaaf in "Schwarzwalduhren", provides his own research which leads to the earliest cuckoos being in the "Franken-Niederbayern" area (East of Germany), in the direction of Bohemia (a region of the Czech Republic), which he notes, lends credence to the Steyrer version.
The legend that the cuckoo clock was invented by a clever Black Forest mechanic in 1730 keeps being told over and over again. But all of this is not true! The cuckoo clock is much older than clockmaking in the Black Forest. As early as 1650 the bird with the distinctive call was part of the reference book knowledge recorded in handbooks.
Although the idea of placing a cuckoo bird in a clock did not originate in the Black Forest, it is necessary to emphasize that the cuckoo clock as we know it today, comes from this region located in southwest Germany whose tradition of clockmaking started in the late seventeenth century. The Black Forest people who created the cuckoo clock industry developed it, and still come up with new designs and technical improvements which have made the cuckoo clock a valued work of art all over the world. The cuckoo clock history is linked to the Black Forest.
At the beginning of the 19th century the now traditional Black Forest clock design, the "Schilduhr" (shield clock), which had a painted flat square wooden face, behind which all the clockwork was attached. On top of the square was usually a semicircle of highly decorated wood which contained the door for the cuckoo. There was no cabinet surrounding the clockwork in this model. This design was the most prevalent for the first half of the nineteenth century. These clocks were typically sold from door to door by "Uhrentraeger" (clock-peddlers) who would carry the dials and movements on their backs displayed on huge backpacks. Shield clocks are one of these creations from the Black Forest that have gained in popularity over the past few years. Each shield clock from the Black Forest region is beautiful and unique and all are wonderful additions to any home. The designs of the shield clocks are fairly basic. Each one features a clock shield in a square shape and a semicircle on top. The wooden shields are hand carved. Shield clocks are very reminiscent of the early 18th and 19th century timepieces. The graceful and elegant shield clock has been a famed product from the Black Forest since its first inception in the 18th century. The paintings today are done with very bright colors that give a strong and bold look to the clock. Just as they were in the earlier days, each one is highly detail oriented and offers a beautiful display of colors and wood that work together to create an awe inspiring look. Although there are shield clocks, as well as cuckoo clocks, that are made throughout the world, none compare in their beauty and traditional looks as those created in the Black Forest. The most popular manufacturers of beautiful German Black Forest shield clocks are Rombach and Haas and Hubert Herr. These and other German manufacturers have been producing fine Black Forest shield and cuckoo clocks for centuries. Each manufacturer produces time pieces that are filled with the traditional history of those created centuries ago. Whether they feature a cuckoo or a quail call, all Black Forest shield clocks are beautiful time pieces that add elegance and historical value to every home that is fortunate enough to have them.
In the middle of the nineteenth century, there were also cuckoo mechanisms combined with the "Rahmenuhr" (framed-clock). As the name suggests, this clock consisted of a picture frame, usually with a typical Black Forest scene painted on a wooden background or a lithograph. The cuckoo was usually included in the scene, and would pop out in 3D, as usual, to announce the hour.
A skeleton clock is any clock or wristwatch, though typically mechanical in nature, in which the parts that usually conceal the inner workings of the mechanism have been removed or significantly modified so as to display these inner parts.
It is considered to be a showcase design and intentionally exposes to plain view the various gears, wheels and springs within the movement itself. There is no official definition of a skeleton clock per se, but a major portion of the main parts of the timepiece should be openly visible from the front of the clock and most often from the back as well in order for it to be considered and accepted as a skeleton clock. The parts most commonly showcased by a skeleton design are those exhibiting either the most movement or the most attractive design. These may include, but are not limited to the escapement, balance wheel and balance spring, mainspring, and tourbillon. Generally there is either no dial present in a skeleton clock, the dial is clear, or it has been limited to a ring around the edge of the case to provide a mounting surface for the hour markers. In the case of skeleton wristwatches, the back will usually be made of sapphire crystal or another clear material that affords easy examination of the parts protected within both from the front and from behind.
A quartz clock is a clock that uses an electronic oscillator which is made up by a quartz crystal to keep precise time. This crystal oscillator creates a signal with very precise frequency. Usually some form of digital logic counts the cycles of this signal and provides a numeric time display, usually in units of hours, minutes, and seconds.
Chemically, quartz is a compound called silicon dioxide. When a crystal of quartz is properly cut and mounted, it can be made to bend in an electric field. When the field is removed, the quartz will generate an electric field as it returns to its previous shape. This property is known as piezoelectricity.
Many materials can be formed into plates that will resonate. However, since quartz can be directly driven by an electric signal, no additional speaker or microphone is required.
Quartz has the further advantage that it does not change size much as temperature changes. Fused quartz is often used for laboratory equipment that must not change shape as the temperature changes. This means that a quartz plate's size will not change much with temperature. Therefore, the resonant frequency of the plate, which depends on the plate's size, will not change much, either. This means that a quartz clock will be relatively accurate as the temperature changes.
In modern quartz clocks, the resonator is tuning fork shaped, laser-trimmed or precision lapped to vibrate at 32,768 Hz. This frequency is exactly 215 Hz. A very simple electronic circuit can be built with a series of 15 divide-by-2 stages cascaded to get the base time of 1 second. In most clocks, the resonator is in a small can or flat package, about 4mm long. The reason 32,768Hz resonator has become so common is due to a compromise between the large physical size of low frequency crystals for watches and the large current drain high frequency resonators demand from watch batteries. During the 1970s the introduction of Metal Oxide Semiconductor (MOS) integrated circuits allowed a 12 month battery life from a single coin cell when driving either a mechanical stepper motor, indexing the second hand (Quartz Analogue), or a liquid crystal display (LCD Digital). Light-emitting diode (LED) displays for watches have become rare due to their very high battery consumption.
Since the introduction of the low current consumption microprocessor in the late 1970s, clocks and watches now contain a small, special-purpose computer with a program that counts the cycles, and translates them into an electrical form to drive the visible display. The use of computers in electronic timepieces has enabled a wealth of features, such as stopwatches, perpetual calendars, multiple perpetual alarms that play tunes, and other features that would be impractical with simple electronic counters.
The relative stability of the resonator and its driving circuit is much better than its absolute accuracy. Standard quality resonators of this type are warranted to have a long-term accuracy of about 6 parts per million at 31 °C, that is, a typical quartz wristwatch will gain or lose less than a half second per day at body temperature.
If a quartz wristwatch is "rated" by measuring it against an atomic clock's time broadcast, and worn on one's body to keep its temperature constant, the corrected time can easily be as accurate as 10 seconds per year, more than good enough to perform celestial navigation.
Some premium clock designs self-rate. That is, rather than just counting vibrations, their computer program takes the simple count, and scales it using a ratio calculated between an epoch set at the factory, and the most recent time the clock was set. These clocks usually have special instructions for changing the battery (the counter must not be permitted to stop), and become more accurate as they grow older.
It is possible for a computerized clock to measure its temperature, and adjust for that as well. Both analog and digital temperature compensation have been used in high-end quartz watches.
Warren Marrison, working for Bell Laboratories, developed the first quartz clock in Canada. Seiko produced the world's first quartz wristwatch, the Astron, in 1969. The inherent accuracy and low cost of production has resulted in the proliferation of quartz clocks and watches since that time. Quartz timepiece production has emerged from Asia, notably Hong Kong and Japan. Many traditional European clockmakers have continued to produce the less accurate but popular geared timepieces.