Like most natural and technical developments, the accuracy of clocks has increased exponentially over time.
The author of the graphic is the Physikalisch Technische Bundesanstalt PTB in Braunschweig.
1 ms/d → 1 thousandth of a second
1 μs/d → 1 millionth of a second
1 ns/d → 1 billionth of a second
1 ps/d → 1 trillionth of a second
Atomic clock 1
In Germany, the Physikalisch-Technische Bundesanstalt PTB in Braunschweig has been responsible for the time since July 25, 1978. Since we need the time very precisely in our technical world, since 1991 it has been using a cesium atomic clock CS2 according to the SI definition of a second, the accuracy of which is controlled by three other atomic clocks. The long-wave transmitter DCF77 near Mainflingen in Hesse sends a time signal across Europe that is checked by the atomic clock in Braunschweig via a dedicated line. There are also time services via telephone, Internet and satellite.
Atomic clock 2
The rubidium clock PRS10 from 2000, exhibited in the museum, is fascinating because of its size. While the CS2 is the size of a large kitchen fridge, its dimensions are the size of two cigarette packets.
While the CS2 measures one second with an accuracy of approx. ± 10-15 seconds, i.e. with an accuracy of ± 0.000000000000001 second, the rubidium clock comes to ± 10-17 seconds. Nevertheless, the Central European Time will be set with the CS2 for a longer period of time, as the stability of such clocks declines over time.
Why so exactly?
Are our fundamental constants really constant? We can only determine it with a certain degree of accuracy.
There are actually technical applications outside of the basic sciences. Because of their low weight, they can be built into satellites, e.g. they are used to increase the accuracy of the GPS in the future European navigation satellite system "Galileo".
With the help of Einstein's general theory of relativity, heights on earth can be determined much more precisely than before. A clock goes faster in lower gravity - above and below sea level!
And future applications ...?
Greek: chronos = time, meterrein = measure
The chronometer is a precision watch that is finely adjusted in various positions and temperatures, which has been tested at an independent, official test center over a long period of time and has not exceeded defined limit values.
Today the headquarters of the COSC (Contrôle officiel suisse des chronomètres) is in La Chaux de Fonds; it has branches in Biel, Le Locle and Geneva.
(see Callweys Uhrenlexikon, pp. 54-55, 1999 ISBN 3-7667-1353-1)
Recently there is also a chronometer test center in Glashütte.
Image: Large chronometer certificate for a watch from Eterna