I want to use a crystal as the base clock for a watch. Most reference designs I could find use a 32.768 kHz crystal at 20 ppm (parts per million) precision. According to my calculations, this leads to an error of max 52 seconds in a month. After 6 months, that 5 minutes. I would like something better!
There are some solutions I could think of (better crystal, or compensate in SW), but I am surprised not to find any reference online.
Surely I am not the first person to try and address this problem. Do you have any suggestion as to how to deal with this, and possibly reference design?