Robin2:
My cheap Casio wristwatch has an error of about 1 minute in 6 months - I like it to be about 1 minute fast and I only have to correct it when the time changes in March and October. I had assumed that RTC modules would have similar performance....R
Well, Casio has a better quality than most. 99% of all cheap watches and clocks run way too fast because the trim capacitor that would be used to calibrate it is simply omitted. I don't have any experience with the cheap RTC modules, I always just avoided them since the DS3231 is so easy to get.
For a while, I was playing with adding homebrew foil capacitors to cheap clocks, and calibrating them by gradually reducing the capacitance by snipping it shorter with scissors. I have a few that keep +/- a minute a year from that experiment.