Fishman Onboard Aura User Manual page 9

Tuner
With the Play/Edit switch set to Play, depress the Tuner button to turn the circuit
on and off. This digital chromatic tuner accommodates all standard and alternate
tunings and can be activated without an instrument cable. When engaged, the
tuner mutes the output and will turn itself off after 45 seconds.
Note that the tuner is calibrated to A = 440.
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