Before modern clocks were invented, normal people simply didn’t know what time it actually was. If you had to make an appointment, you’d likely just say something like “meet at sunrise.” You probably think that you know the exact time right now just by glancing at the clock on your computer or smartphone, but do you actually? Those are updated over WiFi, and can drift by more than a second. That’s more accurate than most of us will ever need, but if you want a truly precise clock, the Precision Clock MkII 1/2 is for you.
The Precision Clock MkII 1/2 was designed by mitxela to be as accurate as possible to a high degree of precision, while still remaining relatively affordable. It checks the current time from GPS satellites, which in turn receive a highly-accurate UTC (Coordinated Universal Time) from BIPM (International Bureau of Weights and Measures) in Paris. BIPM, in turn, calculates an average time with data provided by timing labs around the world that monitor the time using atomic clocks. That results in a time that is within a few nanoseconds (billionths of a second) of being exact — the trick is just taking advantage of it on a practical clock.
To do that, this clock uses a GPS module to sync with GPS satellites. When it does, an accurate timestamp is sent with every update. That is then shown on a series of seven-segment LED displays with the date and time accurate down to centiseconds (hundredths of a second). mitxela has even compensated for the time it takes signals to be sent from the GPS module to the ATtiny4313 microcontroller, and then to update the display. As mitxela demonstrates, this is incredibly accurate and two Precision Clock MkII 1/2s will always stay in sync without communicating with each other. If you want to build one yourself, mitxela is selling kits.