Vintage E. R. Watts retailer & Son. Optical Square / Vintage Surveyor's Square / Vintage Optical Prisms

retailer We are pleased to present this pocket sized optical square from the 1920's. This device, by E. R. Watts & Son. LTD, allows an observer to see along a line perpendicular to the viewing direction through the use of two prisms. This produces two images, one on top of the other, of the view 90 degrees to the left and right simultaneously.

This novel little item comes in its original card case 7 cm high with a diameter of 4 cm.