This gauge has been designed to facilitate the selection, specification and the final setting of spectacle frames and mountings. Developed at the City University, the scales have graduations in units that correspond to the accuracy required or attainable. The minimum graduations are 2 mm with steps up to a maximum of 5 mm, which is sufficiently accurate for the assessment of head width. 

This gauge consists of an engraved white carrier, a rotatable metal pointer and a slide with a cursor. This instrument is supplied with full user instructions.