From Fender:

Strobo-Sonic Pro® is an ultra precise strobe tuner anyone can use, featuring an astonishing ±0.01 cent tuning accuracy in an incredibly pedalboard-friendly package. Designed with on-stage tuning in mind, the Strobo-Sonic Pro features a large, high-visibility LED display, auto brightness dimming and two easily trackable tuning display modes to provide effortless tuning for any player. Strobe display mode delivers hyper-sensitive accuracy that even the most discerning guitar tech will appreciate, while needle display mode provides a familiar tuning experience for any situation. Conveniently accessible side switches offer deeper control of the reference pitch and three bypass modes including true bypass, buffered bypass and buffered always-on modes.