This app was mentioned in 6 comments, with an average of 2.33 upvotes
I'm wearing my 90's Vostok Capitan. I'm slowly cycling through all my watches and calculating their accuracy with this Android app.
I use an android app called Watch Accuracy (https://play.google.com/store/apps/details?id=sk.kfb.hurban.watch) I compared it to a stopwatch running on my phone and seems very accurate.
You take a picture of the dial and then manually adjust the seconds, minutes, hours and the center point of the hands rotation if needed then save that record.
It supports different profiles for different watches. Some users have issues with a bug that keeps deleting their records but it works fine for me and it is very accurate.
I prefer Watch Accuracy since it can store the exact time on the watch and compare with your phone without delay. I find the other app harder to use since human reaction time is counted as the watches inaccuracy.
https://play.google.com/store/apps/details?id=sk.kfb.hurban.watch
It's called Watch Accuracy. Very easy to use. You take a picture and align the hour, minutes and seconds hands.
https://play.google.com/store/apps/details?id=sk.kfb.hurban.watch
I'll take it down to a shop somewhere and see what happens I guess