meter calibration tone generator, 10 frequencies from 31 to 16000 Hz
sound tone frequency 10 settings in Hz
31, 63, 125, 250, 500, 1000, 2000, 4000, 8000, 16000
no permissions requested with this app
http://www.loggerslunchbox.com/
https://www.kickstarter.com/projects/hannahradcliff/loggers-lunchbox