Lee, T. H. (2008) “It's About Time: A Brief Chronology of Chronometry,” IEEE Solid-State Circuits Newsletter, 13(3). doi: 10.1109/N-SSC.2008.4785780.

• First quartz-controlled wristwatch developed in secret at CEH labs in Neuchatel, Switzerland in 1967

  • CEH: Centre Electronique Horloger

  • Named the “Beta 2” prototypes

    • Exhibited drifts of only a few hundred milliseconds per day

• Sundials have been used since at least 3500 BCE

  • When obelisks appeared for this purpose in Egypt

    • The Luxor Obelisk, 23m tall, is 3300 years old and can still tell the time as accurately as it did when it was built

  • Portable sundials appeared around 1500 BCE

    • At the same time as early water clocks

      • Used a leaky bowl with graduations on inner surface. As the bowl drained over time a person could read what the time was at different water levels

      • Water clocks were then refined, by the ancient Greeks, into clepsydras around 325 BCE

        • Clepsydras means “water thieves”; they were called this because of the outflow of water

      • Water clocks were again refined with a succession of Chinese water towers

        • Between 200 CE and 1300 CE

        • The last of these operated bells and other mechanical indicators

  • Because time was measured using long periods, such as a day or a lunar month, it was always difficult to accurately mark time in fine increments

    • The natural processes used for measuring were dependent on lots of, sometimes inconsistent, variables

      • The length of a day would change according to the time of year etc

      • Water clocks would be affected by the temperature of the water

        • They could even freeze if it got too cold

      • Partial solutions were devised

        • Surrounding sundials with an array of marker stones to allow for resolving shorter intervals

        • Substituting mercury for water

• Technologies appeared abruptly in Europe around the 13th century which revolutionised timekeeping

  • David Landes, a historian, argues that Europe was the centre for this revolution because time needed to be more granular because of:

    • The growth of a professional class which needed to charge for services on a finer-grain basis than by a lunar month;

    • And the Catholic Church which has an arbitrary schedule of prayer and other liturgical activities

  • First examples of clocks designed to fix this appeared in late 13th century and early 14th century

    • Richard of Wallingford’s (c. 1330) provides earliest known description of a weight-driven clock that uses an escapement

    • Giovanni de Dondi’s (c. 1370) contains first drawing of an escapement

    • The invention of the escapement allowed timekeeping to move away from continuous processes to artificial processes that had shorter and freely chosen time constants

• Verge-and-foliot dominated escapement mechanisms for 400 years

  • Uses force from hanging weights to apply constant torque to the axle of the crown wheel

  • The crown wheel has saw-tooths that hit palettes attached to the verge which goes next to the crown wheel

    • The teeth allow for the wheel to be turned discontinuously by alternately hitting one of the 2 palettes

      • A saw tooth hits one palette, causing the verge to rotate until the other palette hits a saw tooth on the opposite side of the crown wheel, which causes the verge to rotate the other way

      • Every time the crown wheel encounters a palette, it is stopped briefly and the torque on the axle forces a restart. The palettes, therefore, cause stops at specific points and produce a periodic intermittent rotation of the verge

  • The foliot was added to allow for people to adjust the clock’s speed

    • A foliot is a bar that sits atop the verge and has weights to control the inertia on the verge

  • This escapement could be used to extend or reduce a unit of time very easily, for example a second according to this escapement could vary greatly depending on the position of the weights on the foliot

  • Verge-and-foliot clocks were not very stable in their timekeeping, often resulting inaccuracies of up to an hour over the course of a day

    • The Salisbury Cathedral clock, built in 1386, drifts a large fraction of an hour per day

      • Like other clocks of the period, this clock has no face and instead chimes every hour

• In the 15th century some soldiers were still using roosters as alarm clocks, so the accuracy of the verge-and-foliot was a great improvement, even if it was inaccurate

• Language:

  • The word clock comes from the Latin word which means bell

    • Similar to other languages that also adopted as a base:

      • Glocke (German)

      • Klocke (Dutch)

      • Cloche (French)

      • This also shows that early clocks were used everywhere in Europe

    • Prior to the mid-14th century the Latin term had applied to all timekeeping devices

      • This changed when escapement-controlled devices were seen as much more accurate and so they needed a new word to distinguish them

• In the 16th century spring drives were introduced, to replace suspended weights, and allowed for more compact shapes

  • Peter Henlein constructed the first

• The pendulum clock came about in the 17th century and quickly became the main timekeeping device across the world

  • Improved accuracy from the verge-and-foliot

    • Verge-and-foliot suffered from friction, as the crown wheel spent a lot of time in contact with the palettes, as well as the fact that its oscillation frequency is a function of several variables that are difficult to keep constant

    • The pendulum, due to its frequency (for small angular displacements) being constant no matter the amplitude and only depending on its length, could act as a more accurate way of managing the escapement

  • Galileo observed in 1602 that a pendulum’s oscillation period was independent of the size of the arc in its swing

    • All that affected a pendulum’s oscillation period was the length of the pendulum itself

  • Christiaan Huygens later realised an error in Galileo’s conclusion and found that the size of the arc does matter, however, for small enough arcs it becomes irrelevant

    • He used this information in 1656/1657 to get Salomon Coster to develop the pendulum clock which replaced the aperiodic weighted foliot with the resonant pendulum

  • Pendulum clocks only had error margins of a few minutes per day

  • The initial problems found in pendulum clocks were due to the legacy verge escapement which, due to the required 90-degree spacing of the palettes, needed the pendulum to make very large swings

    • These large swings caused the pendulum’s oscillation arc to be affected by the amplitude and caused inaccuracies

    • The anchor escapement, developed by Robert Hooke in 1657, allowed for the pendulum to swing in much smaller arcs

      • This greatly increased the timekeeping stability and meant that errors were now only in tens of seconds per day

  • The pendulum suffered from sensitivity to the temperature of its materials, which caused them to expand and change the pendulum’s length, thus changing the oscillation period

    • George Graham, in 1721, fixed this by using a combination of metals

    • This improved the stability even more and errors were only recorded in seconds per day

  • John Harrison made more improvements, compensating for the motion, and created clocks with errors of 250ms per day

    • He also solved the “longitude problem” with the marine pocket watch H4

  • Later pendulum clocks were also operated in a vacuum to reduce damping by air

  • Finally, the energy required to move the indicator became the main culprit for the remaining error

    • William Shortt created, in 1921, a system that used 2 pendulums: a master and a slave. The master ran the clock whilst the slave would operate the indicator

    • This timepiece was so accurate that it was used to discover the instability of the Earth’s rotation

• Piezoelectricity is where you can induce polarization in crystals by applying mechanical stress

  • Originally discovered by Pierre and Jacques Curie in 1880, they also found with Gabriel Lippmann that, due to thermodynamics, the opposite would also be true

  • This meant that by applying a voltage through the crystal it would cause mechanical deformation

  • In 1914 the need to detect submarines led to a sonar system that used quartz ultrasonic transducers, designed by Paul Langevin

    • Not used but established piezoelectric technology

  • Walter G. Cady also worked on a sonar system and after the war discovered that piezoelectric crystals could be used as resonators

    • Cady and George Washington Pierce developed an oscillator that uses a vacuum tube and a crystal resonator

      • Incredibly accurate

• The Accutron wristwatch used an electromagnetic turning fork as a resonator. It then fed power back into the turning fork with a single-transistor circuit to maintain oscillation

  • This was because the demand for wristwatches increased greatly around the world wars

  • The watch hummed instead of ticking

  • Could oscillate at up to 360Hz

  • Offered for sale in 1960

• The Japanese company Seiko began secretly developing watches that used 8192Hz quartz crystals as resonators

  • CEH also chose to use these quartz crystals

  • Astrons, developed by Seiko, used lots of components and so were difficult to produce. This resulted in only 200 ever being sold

    • However, they introduced the world to quartz controlled watches

    • They were put on sale on 25 December 1969

• CEH took over and released the Beta21 model in April 1970

  • These were easier to produce than Astrons as they utilised IC technology

    • An IC is an integrated circuit

• LED watches were introduced in 1973

• Staudte Statek developed a quartz resonator that was much smaller but still accurate and could oscillate at 32.768kHz

  • The standard today

 

Ward, F. A. B. (1972) Clocks and watches. London: H.M.S.O (A Science Museum illustrated booklet).

• In 1088 CE Su Sung set up an elaborate water clock in China using buckets

  • Water flowed into a succession of buckets that were mounted on a wheel

  • As the buckets filled it tipped a balance and caused the wheel to move

• First mechanical clocks appeared in Europe around 1280

  • These were controlled by a cyclic mechanical motion that constantly repeated at equal intervals of time

  • The purpose of these was to inform the townsfolk of the time by striking on the hour

    • They were primarily installed in cathedrals, abbeys and churches

• Giovanni de Dondi built a clock in 1364 that told the time as well as showing the movements of the moon and the known planets at the time: Mercury, Venus, Mars, Jupiter and Saturn

  • Made of brass and bronze, unlike others of the time that were made of iron

• All early mechanical clocks were driven by heavy weights being suspended, allowing that potential energy to go into the clock and be controlled by the escapement

• In time clocks were made out of brass and eventually wood

• The long-case clock, or grandfather clock, lasted between 1660 to 1800

  • Its form remained unchanged, after the invention of the anchor escapement, but its appearance changed with fashion

• Big Ben was constructed in 1859 and has an escapement that allows its timekeeping to be independent of the effects of wind and weather on the exposed hands

 

Fenna, D. (2002). calendar. In A Dictionary of Weights, Measures, and Units. : Oxford University Press. Retrieved 27 Oct. 2022, from https://www-oxfordreference-com.soton.idm.oclc.org/view/10.1093/acref/9780198605225.001.0001/acref-9780198605225-e-202.

Calendar

• A calendar is a scheme for grouping, labelling and distinguishing individual days

• The Moon and Sun provide groupings that are clear and natural

  • A lunar period (aka a month; caused by the moon) is about 30 days

  • A solar period (aka a year; caused by the sun) is about 365 days

    • About 12 lunar periods

• A synodic period is the time it takes for a celestial being to be in-line with both the Sun and the Earth

  • A synodic month is the length of time it takes for the moon to do a full circle of the Earth

    • On average: 29.53059 days approx.

• A tropical year is the time it takes for the Earth to fully circle the Sun

  • On average: 365.24222 days approx.

    • Hence: 1 year = 12.36827 months approx.

• Neither the synodic month or tropical year are an exact number of days, nor is the year an exact multiple of the natural month

  • Adaptions have been made in calendars to accommodate this

    • The familiar calendar adheres closely to the natural year

      • Including months of relatively arbitrary size as well as leap years

    • Jewish and Muslim calendars incorporate the natural month but the natural year doesn’t quite fit

• The leap year was added into the familiar calendar to accommodate for the 0.24222 days that take place in every natural year

  • Added so that the calendar would stay in time with the seasons

  • Added by Julius Caesar in the year 45 BCE

  • It is an extra day in February, which was (at the time) the last full month of the year that started at the spring equinox, every 4 years

    • This equated the year with 365.25 days and allowed for the calendar to only lose accuracy, by one day, every 128 years

• As time went on the year, according to the Julian calendar, became out of sync with the seasons

  • By the 16th century this amounted to around 13 days

  • Pope Gregory XIII adopted the Gregorian calendar, for the Roman Catholic Church, to fix this

    • The Gregorian calendar had leap years not occurring in years that were multiples of 100 unless they were multiples of 400. This excludes 3 days per every 400 years and equated the year with 364.2425 days approx..

      • This meant the calendar would only lose a day every 3,323 years

      • The calendar also excludes leap years from occurring on years that are multiples of 4,000

        • Thus meaning the calendar only loses a day of accuracy every 20,000 years

• Since the tropical year is 365.2422 days approx.. then equal seasons would last 91.31 days approx..

  • However, the Earth’s orbit is elliptical and so seasons differ in length from one another by a few days

• The Gregorian calendar took a long time to be adopted by the whole world, with Catholic European countries adopting it quickly but Orthodox countries taking longer, and is still used today

Time

• The natural world has 3 conspicuous units of time:

  • The day

  • The lunar month

  • The year

• Each of these 3 have been accepted as mostly unchanging until recent centuries

  • All are actually lacking in constancy and are changing progressively over time

    • The irregular shape of Earth affects its rotation

    • The elliptical orbit of Earth has a central body (the Sun) at an offset rather than at the geometrical centre

      • Elliptical travel is also not steady in speed

    • The Earth and Moon pair are relatively close in mass so what actually follows the orbital path around the sun is not the centre of the Earth but a moving point which is 4,600km from Earth’s centre towards the centre of the Moon

      • This is called the barycentre

      • It is still situated within the mass of Earth; it is 36% of the Earth’s radius away from Earth’s centre-point

• Key natural unit of time is the solar day

  • This is the value of observed time between consecutive high noons

  • The day, according to our clocks, is the average of this observed time over consecutive days

  • This can then be divided into 24 (mean solar) hours

  • Time based on this is referred to as (mean) solar time

• Sidereal time is calculated based on the revolution relative to fixed stars

  • More accurate than mean solar time

  • There are 366 sidereal days in a 365 normal day year

    • Because sidereal time accommodates for the rotation that is “lost” by traversing an orbit

• Atomic time is based on the oscillations of the atom caesium-133

  • A day, according to atomic clocks, is 86,400 seconds

  • Established the second as the key unit of time, rather than a fraction of a day

  • Established in 1967

  • Provides the basis for universal time