iGeiger is a ratemeter program. It uses the microphone to detect the clicks from your geiger counter (or other device) and display the Counts Per Minute (CPM).
The measurement period can be set between 1 and 3600 seconds, and readings can be optionally normalized to one minute (60 seconds). The displayed value is grayed out until
an entire measurement periods worth of readings has been accumulated.
The minimum required volume of a click to be detected (threshold) can be set, as well as a delay time between clicks.
Readings are graphed, and they can also be stored in a text file that can be accessed via the iTunes file sharing feature. Your location can optionally be included in the recording reading, as well as a timestamp and the CPM reading.