Optical flat, with case, glass / leather / velvet / metal, made by Lapmaster, c. 1960, used by Ross Simpson Engineering, Sydney, New South Wales, Australia, 1963-2007
The optical flat is a thick clear glass disc with top and bottom surfaces polished flat, bevelled upper and lower edges and frosted cylindrical side. The flat is stored in a square grey and green leather covered case with blue velvet lining. The flat fits into a cylindrical recess in the case on top of a blue fabric tab which when pulled allows the disc to be easily removed. The case has two hinges at the back and one clip latch at the front. Marked on top of case.
Three arrow heads (carets), all pointing the same direction, are lightly etched into (or pencilled onto) the side of the disc.
'M21465 LAPMASTER 1/10 X/2' is etched into the side of the disc.
There is a silver sticker on the upper right of the top outside of the case from the "National Measurement Laboratory" with the CSIRO logo and "CSIRO" under the logo. "Date of Calibration" is printed and "June 1995" is handwritten. "Report No:" is printed and "RS25536" is handwritten.
Above the CSIRO sticker is a black Dymo label imprinted "M21465".