Proportionscope (5.12)
The proportionscope, first designed and manufactured by GIA in 1967, is an instrument that casts a silhouetted image of the diamond It allows us to check the proportions of the stone in question. More current technology has largely replaced this but still a handy gemological tool to include in one’s lab.
Courtesy of: http://www.minedirect.com/EnlargedPages/Equipment/Misc/PS-1.html