Equinox Headstock Tuner Black. The D'Addario Equinox Headstock Tuner precisely tunes guitars, basses and other stringed instruments utilizing vibrations rather than sound. Using a highly sensitive piezo sensor and large multi-color display, the Equinox Headstock Tuner allows you to tune easily and accurately in noisy and dimly lit environments where many other tuners fail. The tuner features a pivoting display.