One counter reads in the plus direction and another in the minus directiion, so incremental measurement can be made in either direction
Carbide tipped scriber
Made of stainless steel (except the base).
With driving wheel. With dial test indicator holder.
Supplied with dust cover
Optional accessory: clamp for protracotors (code 2372-CLAMP)

3M 00584 Scotch-Brite Surface Conditioning Belt, SC-BS, A/O Medium, 3 in x 118 in, 7010365595
Dynabrade 92585 3-1/2" Dia. x Medium Hook-Face Surface Conditioning DynaBrite Disc, 10/pack
Dynabrade 90873 2" Dia. Medium NWN DynaBrite Locking-Type Disc, 25/pack
3M 77197, Scotch-Brite™ Roloc™ Deburr and Finish PRO Unitized Wheel,TR, 3 in x 1/8 in x NH, 8C CRS+, 7100109130, 40/box
3M 65033, Scotch-Brite Diamond Wheel, 645DC 6 in x 1/2 in x 1 in, 7010365574, Box of 3
3M 26016, PPS Series 2.0 Adapter, Type S9, 16 mm Male, 1.5 mm Thread, 7100135330 
