Guitar Mate Clip-on, for acoustic and electric guitars cherub - Model Name: Guitar Mate WST-500G - Features: Clip-on - Power: Uses CR2023 button battery Accurate tuning with minimal external noise interference Operation is simple with only a power switch and a flat switch This item was stored by my parent for many years and is now being offered for sale. The button battery is included. When the power switch was turned ON, the power seemed to turn on, and the lamp lit up (last photo). I don't own a guitar myself, so I don't know how to use it very well... (I'm sorry) Thank you for looking.