Good fun but obviously not a professional tool

Dont expect miracles but this is quite cute and sort-of works.

The mode with the graph (as in last picture, grey) is the most useful, as the position of the peaks is constant even if the app changes its mind about which to call the primary one.

Not updated for iPhone 5 or 6 screens, but works on my 5s.

improbable22 about PocketMeter, v1.1.0