About the D'Addario Nexxus 360 PW-CT-31 USB Rechargeable Tuner for Viola:
 
The Nexxus 360™ Rechargeable Viola Tuner offers the fastest, most accurate tuning for violists. It features an extra bright, full-color LED with 360-degree adjustability for the perfect viewing angle and screen clarity in any lighting. From the classroom to the stage, enjoy up to 24 hours of tuning and an auto power-off setting to help you maximize each charge. The Nexxus 360's piezo reads vibrations and is optimized for orchestral stringed instruments, and offers our widest hertz range—from 415 to 465Hz. For best accuracy on viola, attach the tuner on any part of the shoulder with the non-marring clamp. 1 ft USB-C cable included.