For some scientific work timing of the utmost accuracy is essential. It is also necessary to have a standard of the maximum accuracy against which working clocks can be calibrated. An ideal clock would give the time to unlimited accuracy, but this is not realisable. Many physical processes, in particular including some transitions between atomic energy levels, occur at exceedingly stable frequency; counting cycles of such a process can give a very accurate and consistent time—clocks which work this way are usually called atomic clocks. Such clocks are typically large, very expensive, require a controlled environment, and are far more accurate than required for most purposes; they are typically used in a standards laboratory.
For some scientific work timing of the utmost accuracy is essential It is also necessary to have a standard of the maximum accuracy against which working clocks can be calibrated An ideal clock would give the time to unlimited accuracy but this is not realisable Many physical processes in particular including some transitions between atomic energy levels occur at exceedingly stable frequency; counting cycles of such a process can give a very accurate and consistent time—clocks which work this way are usually called atomic clocks Such clocks are typically large very expensive require a controlled environment and are far more accurate than required for most purposes; they are typically used in a standards laboratory