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
The Citizen men's watch Radio Controlled AT8260-18A is a perfect combination of elegance and precision. With a diameter of 43mm and a stylish silver-tone stainless steel case, this watch is a timeless addition for men. The white dial is accentuated by clear line indices and gives the watch a classic aesthetic. The high-quality blue leather strap not only offers a high level of comfort, but also a touch of color and individuality. The watch is equipped with the precise H800 caliber and has impressive features such as a power saving mode and an amazing 180 day power reserve. The radio clock function allows the time to be automatically adjusted in different time zones, including EUR, JPY, USA and China. The Citizen AT8260-18A is waterproof up to 10 bar, meaning it is ideal for everyday use as well as leisure and water sports activities. The sapphire crystal protects the dial from scratches and ensures long-lasting clarity. With a 22mm lug and a low case height of just 10mm, this watch offers a secure fit and a slim profile on the wrist. The Citizen men's watch Radio Controlled AT8260-18A embodies quality, style and precision and is the perfect choice for today's modern man. Elegant diameter of 43 mm Precise and timeless for men Analog chronograph with caliber H800 White dial with clear line indices Impressive power reserve of 180 days 10 bar water resistance for versatile use Robust sapphire crystal protects against scratches Stainless steel housing in stylish silver High quality blue leather strap for comfort 22 mm lug width for a secure fit Low housing height of only 10 mm Caliber functions: energy saving mode, 180 days power reserve, radio controlled watch - EUR - JPY - USA - China, +/- 15 sec per month accuracy , time zones available and world time function
Garmin Epix™ Pro Gen 2 Sapphire 51mm Black/Carbon Gray Titanium with Silicone Strap 010-02804-01Discover a smartwatch that knows no compromises with the Garmin Epix™ Pro Gen 2 Sapphire 51mm Black/Carbon Gray Titanium 010-02804-01. This watch is the ultimate for athletes and adventurers who value a premium wearable that impresses with both functionality and aesthetics. Performance meets luxury The exquisite design of the Garmin Epix™ Pro Gen 2 Sapphire with its 51mm metal case made of fiber-reinforced polymer, framed by an elegant bezel and cover made of titanium, speaks for itself. Added to this is the bright, 1.2-inch AMOLED touch display, which impresses not only with its scratch resistance, but also with its vibrant colors and deep black tones. A battery life that keeps up with you With up to 10 days in smartwatch mode and up to 20 hours in GPS mode The Garmin Epix™ Pro Gen 2 Sapphire accompanies you through your longest adventures without having to worry about the next charge. Illuminated in the dark Whether you're getting up early or training at night, the integrated LED flashlight with variable intensity levels and red safety light always offers you one clear view and security. Train with Intelligence The Hill Score and endurance value, based on your VO2max and training history, give you valuable insights into your performance and progress, while tackling steep climbs or putting your endurance to the test. Health and fitness - hand in hand With extensive health and fitness functions, combined with the training readiness indicator, which is based on a variety of health data , the Garmin Epix™ Pro Gen 2 Sapphire is your personal health coach on your wrist. Robust and reliable Designed to meet the strictest US military standards, this smartwatch is your indestructible companion for all challenges - whether in the wilderness or the urban jungle. Intuitive navigation and connectivity SATIQ™️ technology and multi-frequency reception ensure precise route recording. At the same time, you always stay connected thanks to Smart Notifications. The Garmin Epix™ Pro Gen 2 Sapphire is not just a timepiece - it is a statement, a tool and a loyal partner for all your endeavors. Experience the symbiosis of the most advanced technology and sophisticated design. Make a statement with the Garmin Epix™ Pro Gen 2 Sapphire 51mm Black/Carbon Gray Titanium 010-02804-01 and don't compromise on style or performance. Brilliant AMOLED touch display Integrated LED flashlight Up to 10 days of battery life Advanced training values Health and fitness features SATIQ™️ Technology Exclusive titanium design Robust and military standard tested Training readiness display Morning report adjustments Multi-frequency GPS Garmin Coach Integration
The fēnix® 8 multisport smartwatch is ideal for ambitious athletes and outdoor enthusiasts who want to push their limits. This advanced smartwatch offers numerous features to help you optimize your performance and keep track of your health data. With its bright AMOLED touch display, a battery life of up to 16 days in smartwatch mode and numerous innovative features, including speaker and microphone integration as well as an integrated LED flashlight, it is perfect for any challenge. The exclusive design of the fēnix® 8 is both robust and functional, with waterproofing, a metal sensor protector and optional scratch-resistant sapphire crystal. It is tested to US military standards and suitable for extreme conditions. You can make calls directly from your wrist, use your smartphone's voice assistant and activate specific watch functions offline using voice commands. For athletes, the fēnix® 8 offers special training plans for various sports, detailed performance analysis and innovative functions such as PacePro™ and ClimbPro. The smartwatch also supports multi-sport activities with auto-switching, providing precise data for a variety of sports including diving, HIIT and ski touring. The fēnix® 8 not only impresses with its sports and fitness functions, but also with comprehensive navigation options with Outdoor Maps+, SatIQ™ technology and ABC sensors. It offers a variety of health and safety features such as the Morning Report, Body Battery™ and stress level measurement. With the Garmin Connect™ app you can always stay up-to-date, personalize your smartwatch and analyze your health data. The smartwatch also enables contactless payments with Garmin Pay™ and listening to music without a smartphone. fēnix® 8 multisport smartwatch, robust watch for sports and outdoors fēnix® 8 multisport smartwatch The fēnix® 8 multisport smartwatch is ideal for ambitious athletes and outdoor enthusiasts who want to push their limits. This advanced smartwatch offers numerous features to help you optimize your performance and keep track of your health data. With its bright AMOLED touch display, a battery life of up to 16 days in smartwatch mode and numerous innovative features, including speaker and microphone integration as well as an integrated LED flashlight, it is perfect for every challenge. The exclusive design of the fēnix® 8 is both robust and functional, with waterproofing, a metal sensor protector and optional scratch-resistant sapphire crystal. It is tested to US military standards and suitable for extreme conditions. You can make calls directly from your wrist, use your smartphone's voice assistant and activate specific watch functions offline using voice commands. For athletes, the fēnix® 8 offers special training plans for various sports, detailed performance analysis and innovative functions such as PacePro™ and ClimbPro. The smartwatch also supports multi-sport activities with automatic switching, providing precise data for a variety of sports, including diving, HIIT and ski touring. The fēnix® 8 not only impresses with its sports and fitness functions, but also with comprehensive navigation options with Outdoor Maps+, SatIQ™ technology and ABC sensors. It offers a variety of health and safety features such as the Morning Report, Body Battery™ and stress level measurement. With the Garmin Connect™ app you can always stay up-to-date, personalize your smartwatch and analyze your health data. The smartwatch also enables contactless payments with Garmin Pay™ and listening to music without a smartphone. Bright AMOLED touch display Up to 16 days of battery life in smartwatch mode Integrated LED flashlight Speaker and microphone for voice functions Sport-specific training plans 24/7 health and fitness features Optimized map navigation with Outdoor Maps+ SatIQ™ technology for precise route recording Multisport auto-switching for seamless activities Garmin Coach Adaptive Training Plan Integrated surfing app and MTB dynamics HIIT workouts and animated trainings on the display Heart Rate Monitoring and Pulse Ox Sensor Garmin Pay™ for contactless payments Garmin Connect™ app for comprehensive data analysis Music streaming from Spotify®, Deezer® or Amazon Music Turn-by directions and POIs along the route Women's Health Tracking Jet lag travel guide Floor and height detection Stock tracker for up to 50 stocks Health Snapshot™ for health verification
The Seiko Astron GPS Solar Chronograph SSJ023J1 brings a distinctive design together with advanced technology. The dial carries a celestial motif that recalls the grained surface of a planet, the Earth as seen from above. Skeletonised hour and minute hands and substantial indices improve legibility. The two layer bezel in contrasting metals gives the watch a forward looking appearance, while the bevelled bracelet catches the light. The calibre 3X62 holds an accuracy of ±15 seconds per month and runs for around six months on a full charge. Functions such as a perpetual calendar and automatic hand adjustment make it as capable as it is good to look at. Water resistant to 10 bar and fitted with a screw case back, it is a watch for any occasion. Calibre 3X62, GPS solar Accuracy of ±15 seconds per month Power reserve up to 6 months Water resistant to 10 bar Celestial dial motif Two layer bezel in contrasting metals Perpetual calendar and automatic hand adjustment LumiBrite on hands and indices
The Seiko models SSH165J1, SSH167J1 and SSH169J1 combine a lasting design with current technology, drawn from the legendary 1972 chronograph. Watches of this kind became a first choice for pilots and racing drivers, who depend on technical ability and solid construction. The GPS solar drive holds an accuracy of ±15 seconds per month, and a full charge lasts around six months. The dual time function and the world time function for 38 cities add further flexibility. The stainless steel case with super hard coating and the double domed sapphire crystal with super clear coating stand for durability and clear reading alike. With 10 bar water resistance and a screw case back, these watches are equipped for everyday demands. Calibre 5X83, GPS solar Accuracy of ±15 seconds per month Power reserve up to 6 months Stopwatch: 12 hours in steps of 1/20 second World time function for 38 cities Stainless steel case with super hard coating Double domed sapphire crystal with super clear coating Water resistant to 10 bar
The Garmin fēnix® 8 Pro multisport GPS smartwatch is the ideal companion for athletes who want to stay connected during outdoor activities and optimize their performance. With its unique combination of functionality and high-quality workmanship, it offers a first-class experience for every type of sport and outdoor activity. Equipped with a vibrant AMOLED display, a robust titanium bezel, and scratch-resistant sapphire glass, the watch impresses with its brilliant and robust design. As a special innovation, Garmin integrates inReach technology for the first time, which enables both satellite and LTE connections, ideal for SOS emergency calls or two-way communication in challenging environments. The fēnix® 8 Pro is also equipped with over 80 sports apps and offers intelligent performance and health features to help you achieve your training goals. With an impressive battery life of up to 27 days in smartwatch mode and water resistance up to 40 meters, it is optimally equipped for any challenge. Premium multisport GPS smartwatch with AMOLED touch display Integrated inReach technology for LTE and satellite connections Robust design with titanium bezel and sapphire glass Over 80 sports and outdoor apps Titanium bezel, sapphire glass, and bright LED flashlight Sport-specific strength and endurance training plans Intelligent performance and health features Battery life Up to 15 days in smartwatch mode
The Garmin fēnix® 8 Pro multisport GPS smartwatch is the ideal choice for sports enthusiasts who demand the highest standards from their equipment. This watch combines the latest technologies with a robust design, making it perfect for intense activities. Its integrated inReach technology enables both LTE and satellite communication, significantly improving safety and accessibility in remote areas. Thanks to the AMOLED display and titanium bezel, the watch not only offers excellent visibility and durability but also a sophisticated appearance. Sapphire glass provides additional protection against scratches. The fēnix 8 Pro offers innovative fitness and health features, including sport-specific workouts and navigation options. With an impressive battery life of up to 27 days in smartwatch mode and submersibility up to 40 meters, this watch is perfect for long adventures and extreme conditions. Premium multisport GPS smartwatch with AMOLED display Integrated inReach technology for satellite and LTE connections Robust design with titanium bezel and sapphire glass Over 80 apps and international maps Sport-specific strength and endurance training plans Intelligent performance and health features Battery life of up to 27 days in smartwatch mode Submersible up to 40 meters depth
The Seiko Astron GPS Solar men's watch HAB001J1 combines precise technology with a dynamic design. This watch features a multifaceted titanium case with a striking brushed and polished finish. The octagonal, two-part titanium bezel ensures a low center of gravity, enhancing wearing comfort. The blue dial with horizontally symmetrical subdials features an interlocking triangle pattern, creating a harmonious overall look. An innovative GPS Solar dual-time system keeps precise time, while the quick-release strap system offers flexibility and ease of use. With an impressive battery life of up to 6 months on a full charge, this men's watch is a reliable everyday companion. Faceted titanium case with brushed and polished finish Two-part octagonal bezel for enhanced wearing comfort Innovative GPS Solar Dual-Time System Blue dial with geometric pattern Quick-release strap system Runs for up to 6 months on a full charge Horizontal, symmetrical subdials Enhances functionality and style with Interchangeable wristbands table
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 max bill MEGA Solar 059/2023.02 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 light gray matt, luminous dots with environmentally friendly luminous material. The Junghans max bill MEGA Solar 059/2023.02 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 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.
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 Case base ceramic Ø 40.4 mm, height 8.2 mm. The striking design of the Junghans 18/1000.00 is completed by the dial with a glass dial, dial print and hands with environmentally friendly luminous material. The watch also has a scratch-resistant sapphire crystal and a synthetic rubber strap with a PVD-coated titanium folding clasp.
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.