Bought for my husbands guitar , good little tuner, bright and clear display but most importantly accurate .
Automatically turns off after no signal detected after 3 minutes in tuning mode to save battery life
the battery can be recharged with the supplied USB cable and last approximately 5.5 hours and yellow display indicates flat note, red indicates sharp note the blue indicates the correct note
https://www.amazon.co.uk/Mugig-Metronome-Rechargeable-Battery-Lasting/dp/B01DPAFZVK