"Rectangular Graphometer By Gourdin - 1781"
Unusual shape for a French brass graphometer from the 18th century. It is signed and dated “Gourdin at the Quarter Circle in Paris 1781”. This graphometer is rectangular, equipped with two water levels, two fixed pinnules and a two-pinnule alidade. On the back, it bears no trace of a ball joint or support. It was therefore used directly placed on the board or perhaps hung from the side on the board. Thus, the two levels were used in order to place the instrument perfectly flat. We have not been able to find any other similar graphometer, in ancient or modern literature. The condition is excellent. The size is 19×11.8 cm. 
Le Magazine de PROANTIC
TRÉSORS Magazine
Rivista Artiquariato