TickTrackTock

this version has more precise calibration for amplitude measurements

This app requires a bit of dexterity and understanding how other timegrapher devices and apps generally work. This particular one relies on the excellent microphone which is already built-in to your iphone. You need a relatively quiet place to do this. The iPhone best picks up the sound when it is dressed in a protector and you put the bottom side of the phone onto the dial of the watch. You need to manually set the beat-per-hour for your watch. Typically it is 63600 = 21,600 for the mainstream watches, and sometimes 83600=28,800 for some better models. If you do not not know it, don't worry: as soon as you start you should be able to see the beats of the watch on your screen and count exactly how many times it beats in a second - that is the width of the display - then multiply the number of ticks you see by 3600 to get the beats-per-hour number. The lower display has advance/retard line. You can pull it up or down with your finger and align it to zero at the left of the screen, then read off the deviation of the watch per 24 hours on the right side, just like in other timegrapher devices and applications. Please see the screenshots to get an idea of what you are supposed to see.