The tool is a portable tuning fork for Android devices
A440 (A 440 Hz) is an international standard (ISO 16) for tuning musical instruments setting the frequency of the note "La" of the first octave to 440 hertz.
For the first time a frequency "La" of the first octave of 440 Hz was recommended everywhere by an international conference in 1939.
In 1955 this compliance was enshrined in the international standard ISO 16.