Here it is, folks. The volume knob, otherwise known as an auxiliary potentiometer (aux. pot).
This knob can be used as a nice alternative to button pressing when setup to control pedal assist level. It can also be programmed to control other things.
More info from Grin:
"5kOhm Auxilliary Input Pot for CA3 devices with CNC machined aluminum handlebar clamp for securing to 22mm (7/8") handlebars. Allows you to adjust any of the speed, power, current, or PAS levels on-the-fly while riding. Manufactured in Canada with IP67 waterproof potentiometer."