D’Addario Rechargeable Nexxus 360™ Headstock Tuner offers fast, accurate tuning without the cost and hassle of replacing batteries. the discreet, clip on design features 360 degree rotation, plus a super bright, full color LED display, assuring a perfect viewing angle and screen clarity in any lighting. Simply plug the supply to USB cable and any USB power device as needed and enjoy 24 hours of tuning time per charge.