These scales are used with optical tooling instruments to measure the precise distance of any object from the line of sight.  Then, since the line of sight effectively establishes an extremely straight reference line, alignments between different objects (such as machine components, foundations, rollers, etc.) are quantifiable.
Brunson and K&E scales have optical targets evenly spaced every 0.100". The optical micrometer on an instrument works as a vernier, displacing the line of sight laterally. Using this displacement, the reticle is "brought into register" with the nearest target on the scale, and the precise displacement is read directly from the graduated micrometer drum. By adding or subtracting the micrometer's reading from the scale position, a precise measurement is made. 
Made of hardened steel with a white matte surface
Length: 10", 20", 40"
Data Sheet