When you strum a string, it vibrates and produces a sound wave. These waves are measured in Hz (Hertz), and each tone has its own frequency.
With GuitarTuna, you have the option to create custom pitch notations, with the Calibrate feature. Tap on Settings and from the menu that opens, tap Calibrate button.
Tap - or + buttons to adjust the frequency as per your preference. Tapping Reset changes the frequency back to 440 Hz.
By default, the frequency is set to 440 Hz, which is recognized as an international tuning standard. Guiseppe Verdi, an Italian composer, placed A exactly at 432 Hz, which is the most well known alternative tuning.
It's really up to you to choose which frequency suits you best!
