Perspective drawing instrument with three discs - has spindle with two fixed end discs and larger sliding centre disc

摘要

The perspective drawing instrument has three round discs (c, d), through whose centres a spindle (b) passes. Two of the discs (c, c) are fixed to the spindle ends, while the third and larger one (d) slides between them. The spindle ends are movably mounted in a ruler body (a), so that it can tilt about the central disc. The latter forms a guide track with one of the outer ones. The equipment avoids the need for a large drawing board, nor is it necessary beforehand to determine the alignment and datum points.