What does playability mean?

``Playability'' can be defined as the region of a multidimensional space given by the parameters of the model where a good tone is obtained, where by good tone, we usually mean the Helmholtz motion.

• The string sticks to the bow for most of the time, slipping backwards just once per vibration period.

• String motion:
  
  Motion of a bowed string during an ideal Helmholtz motion. String velocity at the bowed point and trasverse force exerted by the string on the bridge.