Digital Clock Radio Not Showing Right Time

[Prudie]

Jackdaw's thread about the speaking clock has prompted me to ask a question I've been meaning to. I have a mains operated digital clock/radio/alarm in the bedroom.
If there's a power cut it always comes back on displaying the right time (almost), similarly as the clock changes it's automatic BUT it's always 3 minutes slow and I have to manually change the time. Why is this?

[SparklyKid]

Gives you time to get dressed perhaps,lol.

[SparklyKid]

Sorry, t'other way round.

[Old_Geezer]

There are clocks, and there are clocks. Radio control will pick up the right time as long as it gets the signal. Those that just use the mains frequency may carry on where they left off so a 3 minute power cut will ensure it's 3 minutes slow. Those with battery backup and quartz crystal ought not be effected. Anything else is a mystery.

[Atheist]

OG; affected would be more correct. :)

[Old_Geezer]

Probably: but it feels wrong for inanimate stuff to be affected somehow.