Measure radius of external arc, arc angle of measured surface should be larger than 90?
Resolution .0005″/0.01mm
Buttons: on/off, set, inch/mm, preset (+, -)
Automatic power off, move the digital unit to turn on power
Battery CR2032, Data outputMade of stainless steel
Supplied with pin gage for zero setting

Dynabrade 78599 3/8" Dia. x 2" W x 1/8" Center Hole, 80 Grit, 100/pack
3M 27313, Ultra Durable 5 inch Power Sanding Discs, Universal Hole, 60 grit, 7100187645, 10 per pack
Dynabrade 78128 3" Dia. Coarse NWN VT DynaBrite Locking-Type Disc, 25/pack
3M 15289, 663FC, 2-3/4" X 160", 40u, Diamond Trizact Belts 7010508900 