Testing my home made wind chimes

I bought this to measure the frequency of the tones from a five-tube wind chime I made. My iPhone is a 5C.

The scope display is of little use, but the frequency shown below the scope is stable and spot on. My design was tp produce and E note at 659 Hz; this app measured it at 658 Hz; damned good. I found no other app that offered the measurement of an arbitrary frequency. ANd this was only $0.99

I wonder if the other reviewers that faulted this app have a defective mic.

Ron_Calif about Frequency Counter Pro, v2.0