As the size of workpiece 1 changes during internal grinding, lever 2 turns about fixed axis O and changes the position of plunger 3 with respect to nozzle 4 of the measuring head to which compressed air is delivered. The pressure in the instrument (not shown) depends upon the clearance between the face of the nozzle and plunger 3. This clearance depends upon the size of the hole being ground.
$3932$LHP,M$