Inspecting a surface plate
The electronic level itself is a commercially available item. However, the guide bar and the metal stand on which the measuring levels are placed were made by Mr. Sasaki himself. They are made and used for efficiency without compromising precision.
A surface plate is a work stand with a high-precision flat surface made of metal or stone. The surface plate is also an auxiliary tool for performing measurements, for which the surface plate serves as the standard.
Mr. Sasaki was kind enough to demonstrate how he inspects a surface plate. He takes measurements at equally spaced intervals across the surface plate in four directions: lengthwise, widthwise, and along the two diagonals.
The electronic levels are used in pairs, with a fixed level "A" and a measurement level "B." A is fixed as the point of reference, while B is moved to each measurement point, with its rise or fall expressed in terms of an angle. Although the electronic level must be precisely positioned at each measurement point, the operation proceeds at a brisk pace thanks to the efficient way in which Mr. Sasaki moves. He wears gloves to avoid passing heat from his body to the electronic levels or the surface plate, thus reducing measurement error.
As he checks the unevenness of the surface plate, the measurement readings appear on the digital display in units of one-tenth of a micrometer. Only surface plates that pass this inspection may be used at Nikon production sites.