This is a clip-on tuner for musical instruments. There is no battery leakage in the battery compartment. It shows the same values as other tuners, so I think it's not out of tune. It can be used for guitar, bass, ukulele, violin, etc. The screen turns green when the tuning is correct. Power: 1 x CR2032 (coin battery) Manufacturer's description below: An easy-to-use clip-on auto-tuning meter. By attaching it to the headstock of a guitar, etc., it detects the vibration of the instrument and accurately measures the pitch with ease. In addition to the chromatic mode, which can be used for many instruments, regardless of stringed or wind instruments, you can also switch to dedicated measurement modes for guitar, bass, ukulele, and violin. The bright and large display is also ideal for tuning in dark places.