I have two apps:
1. Watchtracker - to track accuracy of watches. https://itunes.apple.com/lv/app/watc...610666926?mt=8 very easy to use.
2. Timegrapher - as name suggest, it is a timegrapher app you can use with iphone earphone mic. https://itunes.apple.com/us/app/watc...991367080?mt=8 it is not super accurate, but it detects some parameters like beat error and amplitude on par with witschi timegrapher. I doubt you will get acceptable results in noisy shop.