The doozzoo tuner now offers a tuning tone calibration from 415Hz up to 444Hz. Many musicians have asked us for this feature. We are happy to be able to offer that now. With the red slider you can select the tuning tone frequency. With the microphone icon the tuner is switched on. The played tone is displayed and the arrows and the bar indicator gives you hints if the tone is too high or too low. The speaker icon allows you to play tuning tones and the +/- buttons select the tuning tone. Here are the instructions.