Pocket Wall Clock

We've had this unusual wall clock for 22 years. Recently it has stopped telling the correct time and seems to be working in a parallel universe where the usual time has been warped. This is very disorientating as glancing at it over the fireplace, as I have for over 2 decades, no longer gives a real fixed time to base life around.

Don't want to get rid of it as it is part of our lives (and really nice) so I'd better get it fixed