This Bausch & Lomb precision grating includes the original calibration certificate. The box has handwritten notation 'Plano grating for bathtub Ebert'.

Grating size - 110 x 110 mm (ruled 102 x 102 mm)
Substrate thickness and material - 16mm BSC2
Focal length - infinity
Grooves / mm - 600
Blaze angle - 8 degrees 38 minutes
Blaze wavelength - 500nm
Catalog number - 35-53-15-26
Serial number - 646A4B7C3
Coating - Al (?)

This grating appears to be in superb condition. There is a protective cover installed over the grating surface.

Photo set 1664