Yep kodionelli has it 100% right.
It uses the thread pitch of the rocker arm adjuster screw to set the valve clearance. The pointer on the tool is used to make the necessary turn on the screw to precisely set your valve clearance based on screw thread pitch. A full turn of the screw = 1.0mm So your valve clearance, which is 0.1mm, is 10% of 360 degree rotation or 36 degrees. That's why the tool has 36 degree sectors on it
911 Valve Lash Adjustment Tool