Has anyone tried the hairspring app? Apparently you put you mobile device microphone aginst your watch back and it will measure the accuracy based on the ticking. Just wondered if anyone has tried it.
Just given it a quick try ("lite" version). It locked onto the tick of my watch but told me it was 0.0 mins/day fast/slow. I know it gains a few secs per day, so not sure how accurate the app is.