Atomic clock · the current time in Germany
Atomic clock online: the exact time, live on the watch of the month
· 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
What is an atomic clock, and what is rate deviation?
An atomic clock takes its beat from the oscillation of atoms, in Germany from caesium-133 at the Physikalisch-Technische Bundesanstalt in Braunschweig. It deviates by less than one second in 100 million years and is the reference for every clock, whether in your smartphone, in a radio-controlled watch or on this page.
Rate deviation is the number of seconds a watch gains or loses per day. A quartz watch is at about half a second, a good automatic watch at a few seconds, a certified chronometer between minus four and plus six seconds per day.
Test your watch: atomic time runs at the top of this page. Press “Now” when your seconds hand reaches 12 and you see the deviation in seconds. Repeat the test a day later and you know the rate deviation per day.
Last checked: September 2026 · by the RM Time workshop in Solingen
Rate deviation: 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 a watch precisely: 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
Watches that set themselves
A three hand watch that looks after the time itself. It receives the time signal in Europe Japan North America and China and sets itself accordingly including date and daylight saving. Without reception it stays accurate to 15 seconds a month. World time covers 26 cities.This execution is the only one of the four with a warm accent. The dial is ivory with gold tone hands and markers that lift softly off it. Contrast is therefore lower than on the dark dials and the watch reads more as a classic dress watch than as a radio controlled one. It is also the dearest in the series. It fits in with brown leather and with gold on the wrist instead of working against them. Of the four it is the one most likely to be worn with a suit. The ivory also keeps its look under artificial light where white dials can turn grey.The case measures 37.5 mm at 9.25 mm high and is made together with its solid bracelet from Super Titanium. At around 80 g the watch wears accordingly light. Anti reflective sapphire crystal sits over the dial and water resistance is 10 bar.A shock detection function realigns the hands after a knock, the calendar is perpetual and an energy saving mode covers time in the drawer. Calibre H149. Eco-Drive means the watch draws its energy from light. Daylight works just as well as indoor lighting. There is no battery to replace.Radio reception for Europe Japan North America and ChinaAccuracy without signal 15 seconds a monthWorld time for 26 citiesShock detection realigns the handsPerpetual calendar and energy saving modeCase and bracelet in Super TitaniumCase 37.5 mm at 9.25 mm highWeight around 80 gAnti reflective sapphire crystalPower reserve 180 daysWater resistant to 10 bar
For the designer Max Bill, visual sustainability came first. The max bill MEGA Solar joins that ambition with sustainable energy: its highly efficient app connected radio movement is driven by the power of the sun.The 4 recalls an upturned chair, and Max Bill designed the other numerals in square form as well.
A three hand watch that looks after the time itself. It receives the time signal in Europe Japan North America and China and sets itself accordingly including date and daylight saving. Without reception it stays accurate to 15 seconds a month. World time covers 26 cities.This execution sets a dark green into the light titanium frame. Green is rare on radio controlled watches which lifts it out of the crowd without turning loud. In low light the dial reads almost black and only in the sun does the colour show fully. It is the most personal choice of the four. Anyone wearing it picked it for the colour and not because it goes with everything. Against the bright titanium the green also stays legible in a way a dark bracelet would not allow.The case measures 37.5 mm at 9.25 mm high and is made together with its solid bracelet from Super Titanium. At around 80 g the watch wears accordingly light. Anti reflective sapphire crystal sits over the dial and water resistance is 10 bar.A shock detection function realigns the hands after a knock, the calendar is perpetual and an energy saving mode covers time in the drawer. Calibre H149. Eco-Drive means the watch draws its energy from light. Daylight works just as well as indoor lighting. There is no battery to replace.Radio reception for Europe Japan North America and ChinaAccuracy without signal 15 seconds a monthWorld time for 26 citiesShock detection realigns the handsPerpetual calendar and energy saving modeCase and bracelet in Super TitaniumCase 37.5 mm at 9.25 mm highWeight around 80 gAnti reflective sapphire crystalPower reserve 180 daysWater resistant to 10 bar
The sixtieth anniversary of the max bill wristwatches inspired us to create a special edition set. Each watch is packed individually in a case with its own edition design. Together the three of them form the edition set, limited to 1060 pieces.The 4 recalls an upturned chair, and Max Bill designed the other numerals in square form as well.
The Junghans Force Mega Solar is a watch from the Funk & Solar line and impresses with a high-quality multi-frequency radio solar movement J615.84, which supports the following functions: dark power reserve of up to 21 months, sleep mode after 72 hours, large date, convenient time setting via the Junghans MEGA app. The case has the following properties: polished ceramic, ceramic case back, Ø 40.4 mm, height 8.2 mm. The striking design of the Junghans 18/1133.44 is completed by the dial with a glass dial and hands with environmentally friendly luminous material. The watch also has a scratch-resistant sapphire crystal and a ceramic strap with a titanium folding clasp.
Stainless steel meets polished ceramic here. The case measures 41.6 millimetres across at a height of 9.6 millimetres and stays permanently scratch resistant thanks to the ceramic elements on bezel and bracelet. The coated mineral glass back lets light through to the solar cell.The J615.84 multi frequency radio solar movement receives the time signal in Europe, the United Kingdom, Japan and the USA. Fully charged it keeps running for up to 21 months in the dark. The time zone can also be set conveniently through the Junghans app.J615.84 multi frequency radio solar movementRadio reception in Europe, the UK, Japan and the USAPower reserve of up to 21 months in darknessCase of stainless steel and polished ceramicLarge date and perpetual calendarTime zone adjustable via the Junghans appGlass dial with appliques and luminous materialSapphire crystal and water resistant to 10 bar
The Junghans Milano MEGA Solar is a watch from the Funk & Solar line and impresses with a high-quality multi-frequency radio solar movement J615.84, which supports the following functions: dark power reserve of up to 21 months, sleep mode after 72 hours, large date, convenient time setting via the Junghans MEGA app. The housing has the following properties: stainless steel, mineral glass base with vapor coating, Ø 39.2 mm, height 8.4 mm. The striking design of the Junghans 56/4220.00 is completed by the dial with a glass dial with appliques and hands with environmentally friendly luminous material. The watch also has a scratch-resistant sapphire crystal and a leather strap with a stainless steel pin buckle. A Milanese strap is also included.
The Junghans max bill MEGA Solar 059/2021.02 has a connected radio solar movement J101.85 with the following functions: date, convenient time setting via crown or via the Junghans MEGA app in just a few seconds, precise seconds display in half-second increments. The case has the following specifications: titanium, Ø 38.0 mm, height 9.0 and is protected by a curved sapphire crystal, anti-reflective on both sides. The dial has the following features: solar dial matt white, luminous dots with environmentally friendly luminous material. The Junghans max bill MEGA Solar 059/2021.02 is waterproof up to 5 bar. This Junghans watch offers excellent wearing comfort thanks to the vegetable tanned calf leather strap with Alcantara leather base and titanium pin buckle.
The Seiko Astron GPS Solar 2026 Limited Edition, model HAB006J1, is an exquisite men's watch that combines impressive design and innovative technology. Limited to 1200 pieces, it is not only a collector's item but also an expression of style and exclusivity. The dial is inspired by the radiance of the quartz crystal and presents a vibrant pattern that shines through faceted details in a striking rose hue. These facets create a dynamic interplay of light and depth, giving the watch a modern and fresh presence. The watch belongs to the renowned Seiko Astron series, known for its precision and groundbreaking technology: it utilizes GPS solar power, which ensures accurate timekeeping worldwide, down to the second, regardless of location. A particular highlight is the integrated quick-release system of the case, which allows for easy strap changes, a seamless transition from the robust titanium bracelet to sporty silicone. Included in the delivery is a black silicone strap and stylish storage in a recycled nylon case, which underscores the collection's modern appeal. GPS solar technology for precise timekeeping worldwide Dial inspired by quartz crystal structure Limited to 1200 pieces, an exclusive collector's item Integrated quick-release strap system Faceted details in a radiant pink quartz tone Robust titanium bracelet with silicone strap option Exclusive recycled nylon case Ideal for modern and style-conscious individuals Men
The Seiko Astron GPS Solar 2026 Limited Edition impresses with a captivating design inspired by the radiance of the quartz crystal. The dial of this limited-edition men's watch, restricted to just 1200 pieces, reveals a vibrant crystal structure with faceted details that create a dynamic interplay of light and depth. This model is crafted in an appealing green quartz hue, lending the timepiece a clean and modern presence. Functionality is enhanced by an integrated quick-release system, allowing for easy strap changes at the touch of a button, effortlessly switching between a titanium bracelet for technical clarity and a silicone strap for sporty lightness. The striking look is further accentuated by a black silicone strap that highlights the unique aesthetic of the dial. The watch comes in a recycled nylon case, which emphasizes the modern and sustainable character of the collection. Limited to 1200 pieces worldwide Design inspired by the structure of the quartz crystal Quick-release strap system Black silicone strap for a sporty look Green quartz tone for a modern expression Faceted details for dynamic play of light Includes recycled nylon case Movement: GPS Solar
The Seiko Astron GPS Solar men's watch HAB004J1 is an exclusive timepiece, available in a limited edition of only 2,000 pieces worldwide. This model celebrates Seiko's 145th anniversary and is part of the second phase of its anniversary releases. The watch is distinguished by its striking blue details, inspired by "Seiko Blue," a signature color of the 1960s. The HAB004J1 combines modern technology with classic design, offering GPS-controlled timekeeping accuracy and solar power for the highest precision. An ideal example of Seiko's high-quality watchmaking, seamlessly blending tradition and innovation. Limited edition of 2000 pieces worldwide Celebrates Seiko's 145th anniversary Blue details inspired by 1960s "Seiko Blue" GPS-controlled timekeeping accuracy Innovative GPS solar technology Combination of modern and classic design High-quality materials and craftsmanship Exclusive collector's item for watch enthusiasts
The Junghans 1972 Mega Solar men's watch 56/4611.44 is an exclusive tribute to Junghans' long-standing tradition of sports timekeeping. This watch combines a sporting spirit with innovative technology and commemorates the legendary sporting events of the 1972 Munich Olympic Games, where Junghans served as the official timekeeper. With its precise radio-controlled solar movement, the watch requires no battery, as it converts both sunlight and artificial light into energy. Its stainless steel case with a robust titanium bracelet reflects the resilience and elegant style that discerning wearers appreciate. Inspired by sporting tradition and precision Radio-controlled solar movement for reliable operation without a battery Stainless steel case with titanium-coated bracelet Ideal for the sports-loving wearer Easy-to-read dial for maximum clarity Comfortable feel thanks to titanium elements Robust yet elegant design Perfect balance between functionality and style
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
How can I test the rate deviation of my watch?
With the atomic clock on this page. Press “Now” when your seconds hand reaches 12. You immediately see how many seconds your watch is fast or slow. Repeat the test after a day or a week and the difference gives you the rate deviation per day.
How do I set my watch to the exact second?
Pull the crown all the way out when the seconds hand is at 12, set the time to the next full minute and push the crown in at the very moment the atomic time above changes. The guide further down shows every step.
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.
