Atomic clock · Time in Germany
How accurate is your watch?
· Calendar week
In sync with the atomic time of PTB Braunschweig
Deviation of your device: measuring
Technology
How atomic time reaches your wrist
Four ways, one second. A watch from our store for each of them.
Radio-controlled
Receives the DCF77 signal from Mainflingen at night and sets itself. Range around 2,000 km, almost everywhere in Europe.
Deviation 0 s after every sync
GPS watch
Takes the time directly from the satellites, worldwide and without a mobile network. Ideal for travel, time zone included.
Deviation 0 s, worldwide
Bluetooth
Smartwatches and hybrid watches take the time from the smartphone, which in turn follows the network.
Deviation 0 s while connected
Mechanical
Not at all. An automatic watch has no receiver, only balance and hairspring. That is exactly its charm: you set it now and then by this page.
A few seconds per day
How much a watch may deviate per day
| Watch | Deviation per day |
|---|---|
| PTB atomic clock (caesium fountain CSF2) | 0.000 000 03 s |
| Radio-controlled and GPS watch, after every sync | 0 s |
| Quartz watch, typical values | ± 0.5 s |
| COSC chronometer, certified mechanical | −4 to +6 s |
| Tissot Powermatic 80, Nivachron hairspring | a few seconds |
| Automatic without regulation, time for the workshop | over ± 20 s |
The atomic clock deviates by less than one second in 100 million years. Your result from the check above fits in here once you repeat it a day later.
9,192,631,770
Oscillations of the caesium-133 atom have defined one second since 1967.
< 1 s
Deviation of the PTB fountain clock in 100 million years.
77.5 kHz
Frequency of the DCF77 time signal transmitter in Mainflingen.
21,600
Half-oscillations per hour in the Powermatic 80 of the PRX, i.e. six steps of the seconds hand per second.
Setting your automatic watch to the second
The PRX has a hacking seconds function. This is how to use it together with this page.
- Pull the crown all the way out. The seconds hand stops. Best when it is right at 12.
- Set the time to the next full minute. Move the hands slightly past the target minute and back, so the minute hand sits without play.
- Wait for the atomic time above. Watch the seconds line. It fills up to the full minute.
- Push the crown in at the moment the minute changes. The seconds hand starts, now in sync with Braunschweig.
- Check after a week. The one-click check shows how many seconds your watch has gained or lost since then.
Where radio-controlled watches get their time
Every region has its transmitter. Multiband radio watches receive several of them and set themselves when travelling, too.
| Transmitter | Region | Location | Frequency |
|---|---|---|---|
| DCF77 | Europe | Mainflingen, Germany | 77.5 kHz |
| MSF | United Kingdom | Anthorn, England | 60 kHz |
| WWVB | North America | Fort Collins, USA | 60 kHz |
| JJY | Japan | Fukushima and Saga | 40 / 60 kHz |
| BPC | China | Shangqiu | 68.5 kHz |
Casio Multiband 6 and Junghans Mega receive up to six of these transmitters. GPS watches need none of them.
Origin
From the sundial to the atomic clock
Timekeeping begins around 5,500 years ago with the shadow of a rod. Egyptian sundials divided the day into comparable sections for the first time. Since then every new timekeeper has been more accurate than the previous one: water clock, geared clock, pendulum, balance wheel, quartz.
Today the time is delivered to our smartphones, radio alarm clocks and wrists. The reference behind it is always the same: the atomic clock. You can see its time at the top of this page, on the watch of the month.
History
A Nobel Prize and a new second
The idea dates from 1944. The physicist Isidor Isaac Rabi described how the oscillation of atoms can serve as a timekeeper and received the Nobel Prize for it. In 1949 the first atomic clock ran in the USA, in 1955 the first caesium clock with usable accuracy in England.
In 1967 the second was redefined: since then it lasts 9,192,631,770 oscillations of the caesium-133 atom. Today around 400 atomic clocks in more than 60 institutes contribute to International Atomic Time. In Germany that is the Physikalisch-Technische Bundesanstalt in Braunschweig.
How it works
A quartz that is corrected constantly
Every clock needs something that oscillates evenly. In an automatic watch that is the balance wheel, in a quartz watch the quartz crystal. An atomic clock also starts with a quartz oscillator. The difference: its frequency is compared with the resonance frequency of the caesium atoms all the time and adjusted.
The result is a deviation of less than one second in 100 million years. For comparison: a good automatic watch deviates a few seconds per day, a quartz watch a few seconds per month.
Our verdict
Why we still love mechanical watches
An atomic clock is useless on the wrist. But it is the standard against which every watch has to be measured. That it is based on a quartz at its core surprises many. And that an automatic watch like the PRX manages with a few seconds per day, without electricity, radio or satellite, is the real achievement.
If you need the exact second, you will find radio-controlled and GPS watches in our store that set themselves. If you love mechanics, set your watch by this page now and then. Both are a good choice.
From the sundial to Braunschweig
| 3500 BC | Sundials in Egypt divide the day into comparable sections. |
| 1656 | Christiaan Huygens builds the first pendulum clock. Deviation: under one minute per day. |
| 1927 | The first quartz clock is built at Bell Laboratories. |
| 1944 | Isidor Isaac Rabi describes the principle of the atomic clock and receives the Nobel Prize in Physics. |
| 1949 | The first atomic clock runs in the USA, still with ammonia as the timekeeper. |
| 1955 | First caesium clock at the National Physical Laboratory in England. |
| 1967 | The second is redefined via the caesium-133 atom. |
| 1973 | DCF77 transmits the PTB time permanently. Radio-controlled watches become possible. |
| 1999 | PTB puts its first caesium fountain clock into operation. |
| Today | Around 400 atomic clocks in more than 60 institutes form International Atomic Time. This page shows it to you. |
In brief
UTC
Coordinated Universal Time, the reference for all time zones. Derived from atomic time and adjusted to the Earth's rotation with leap seconds.
TAI
International Atomic Time, the weighted average of all participating atomic clocks. Runs without leap seconds.
CET / CEST
Central European Time, UTC plus one hour. Summer time is two hours ahead of UTC.
GMT
Greenwich Mean Time, the historical predecessor of UTC. In everyday use the same as UTC.
Leap second
An extra second that aligns UTC with the slightly varying rotation of the Earth. 27 times so far since 1972.
Hacking seconds
When the crown is pulled, the seconds hand stops. This lets you set a mechanical watch to the second.
Rate deviation
How many seconds a watch gains or loses per day. Normal for mechanical watches, zero for radio and GPS.
Half-oscillation
One swing of the balance wheel. The Powermatic 80 makes 21,600 per hour, i.e. six steps of the seconds hand per second.
That the most accurate clock in the world is at its core a quartz clock that is merely corrected constantly surprises most of our customers.
RM Time workshop
World time
The same second, a different hour
What shows the time here next
Every month a different model from our store runs on atomic time. If you would like to suggest a watch, write to us.
| September | Tissot PRX Powermatic 80 |
| October | Hamilton Khaki Field Mechanical |
| November | Certina DS Action Diver |
| December | Seiko Presage Cocktail Time |
Frequently asked questions
Where does this page get the time from?
Our server keeps its clock in sync with PTB via the NTP time protocol. When the page loads, the server time is transmitted and compared with your device's clock. The display then keeps running in your browser, corrected by the measured deviation.
How accurate is the one-click check?
To about a tenth of a second, limited by your reaction. For a wristwatch that is more than enough. If you need fractions of a second, use a radio receiver or GPS.
Can a mechanical watch show atomic time?
Not by itself. An automatic watch has no receiver. It shows the time you set it to and drifts a few seconds per day depending on the movement. Radio, GPS and Bluetooth watches fetch atomic time automatically.
What is DCF77?
DCF77 is the time signal transmitter in Mainflingen near Frankfurt. It transmits the PTB time on 77.5 kHz and reaches radio-controlled watches within a radius of about 2,000 kilometres. Almost every radio watch in Germany sets itself via this signal at night.
What do CET, CEST and UTC mean?
UTC is Coordinated Universal Time, the reference for all time zones. Central European Time is one hour ahead, summer time two hours.
My watch gains 15 seconds a day. Is it defective?
For an automatic watch that is at the edge of the usual range. Temperature, position and magnetic fields affect the balance. A regulation in our workshop usually brings it down to a few seconds.