Yeah, that's just a shitty (or out of spec) time base. My Seiko watch gains 1-2 minutes a day, but it's completely mechanical so it depends on temperature and winding/mechanism tension for accuracy. There are electronic timing circuits which are resistance and capacity based, and as the resistance and capacitance of the system drift (time/age and temperature) they also drift. A crystal, made to vibrate at high frequency (piezoelectrically, iirc), will provide a much more stable time base and be accurate to seconds over many days' time.

Interesting aside - time keeping is how ships at sea used to determine where they were in the ocean. Latitude can be found from the stars, but longitude can't so it needs a time reference standard. The book, Longitude tells the story of the search and the competing methods for determining location prior to the invention of crystal/electronic time bases and modern GPS. I won't say that the storytelling is particularly gripping, but the actual path to discovery is fascinating.