Caesium is like Quartz, in that it can be used to keep track of scheduled things. However, it is much simpler and hopefully does not have as many bugs. The name derives from the fact that since 1967 the definition of 1 second has been "The duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom." Note: I would have preferred to spell this "cesium," but ...