In the tuning device being described a reference oscillator generates 84 crystal‐controlled frequencies, which follow a stretched scale whose deviations are programmed in an interchangeable diode matrix. Three different diode matrices have been realized, intended for tuning small, medium‐size, and grand piano's, respectively. A bandpass filter is used, the transmission range of which automatically follows the reference frequency. An electromagnetic device is used as a sound transducer. In consequence of this, tuning of all strings on their fundamentals becomes fully feasible. With one medium‐size piano, the achieved accuracy was measured. The accuracy of the tuning with respect to the reference frequency was<10−4in all cases. The total accuracy (including the inaccuracy of the reference oscillator) varies from 10−4for the lowest note to 5×10−4for the highest note.