theres quite alot of engineering that goes into clocks or timekeeping device

changes in the voltage can somehow make the accuracy deviate AFAIK, like for example if you set in clock 1pm to tie with official time, then due to issues with the clock when its 2pm your clock still shows 1.55pm or something like that

thats one of the reason why some watches are so darn expensive, cause their device have to also guarantee super precise timekeeping