The HANG is a new musical instrument (year 2000), suitable for playing with the hands, consisting of two hemispherical shells of nitrided steel. It is the product of a collaboration among scientists, engineers and hangmakers, thanks to which we have been able to better understand the tuning process in all its complexity. Seven notes are harmonically tuned around a central deep tone (ding), which excites the Helmholtz (cavity) resonance of the body of the instrument. There are many ways to play the HANG. We show the different stages of its development over the seven years since its birth in 2000. We describe the tuning process and the musical conception of the HANG.