Most alarm clocks run their internal clock oscillator off of the mains frequency by detecting the peak on each cycle and thus
obtaining their timebase. However not every country uses the same grid voltage/frequency! — This poses a problem, if you’re using a 60hz clock on 50hz, it’s going to run at ~83% of it’s intended speed!
I’ve seen three types of clocks so far, the ones that automagically detect the mains frequency, the ones that allow you to choose with a simple switch, and those that just won’t run at your mains frequency!
For the latter, the following applies: More…