A Short History of Timekeeping: From Sundials to Atomic Clocks

The clock in your browser tab sits at the end of thousands of years of invention. Here is a short tour of how timekeeping became so precise.

By the VClock team at Digimarket Group SIA · Updated 4 November 2026

Sun and shadow

Early civilisations divided the day using the sun. Egyptian shadow clocks and sundials, used for more than three thousand years, told time only when the sun shone, and their “hours” changed length with the seasons.

Water and fire

Water clocks (clepsydrae) measured time by the steady flow of water into or out of a vessel, working at night and indoors. Candle clocks and incense clocks did a similar job by burning at a known rate.

Mechanical clocks

Weight-driven mechanical clocks appeared in European towers around the late 13th and 14th centuries, using an escapement to release energy in regular steps. In 1656 Christiaan Huygens built a pendulum clock that improved accuracy dramatically, from minutes per day to seconds.

Longitude and the marine chronometer

Sailors needed accurate time to calculate longitude at sea. John Harrison's marine chronometers in the 18th century solved the problem, making ocean navigation far safer.

Railway time and time zones

Towns once kept their own local solar time. Railways needed common timetables, so standardised “railway time” spread in the 19th century. In 1884 the International Meridian Conference chose Greenwich as the prime meridian, the basis for the time-zone system used today.

Quartz

A quartz crystal vibrates at a precise frequency when electricity is applied. Quartz clocks (from the late 1920s) and cheap quartz watches (from 1969) made accurate time available to everyone. Most computers still contain a quartz oscillator.

Atomic time

Since 1967 the second has been defined by the radiation of caesium-133 atoms: 9,192,631,770 cycles. Atomic clocks are so stable they would drift by less than a second over millions of years. International Atomic Time and UTC are built from hundreds of them worldwide; leap seconds have occasionally been added to keep UTC close to Earth's rotation.

Your device's clock

Phones and computers synchronise with time servers using the Network Time Protocol (NTP), usually staying within milliseconds of UTC. VClock displays that synchronised system time in your browser — the latest step in a very long story.