As for the key “ B0 zero “ is for reset the Ram swivel base angle to 0 “zero , our CNC slotting machine which Ram can be swivel left and right +/-30 degree for taper slotting purpose , Now CNC-450S which can do taper slotting through Z and Y or X axis moving simultaneously , no need swivel the ram as CNC-350 but we keep the swivel function for CNC-450S and we add a angle encoder for showing the tilting (swiveling) angle purpose. The B axis mean the Ram swivel axis
The B0 zero is for you to set the angle as zero then from the position to calculate purpose. But actually the B0 zero is just for spare function , maybe in the future operator have the chance to use Ram tilting function then the B0 zero angle indicator can help you to read the tilting angle from computer screen.
Attached is the photo showing angle encoder on CNC-450S.