A perspective machine is an optical instrument designed to help artists create perspective drawings.[1] The earliest machines were built centuries ago when the theory of perspective was being worked out, and modern versions are still[2] in use.
^"Perspective Machine", The New and Complete American Encyclopedia, John Low, 1810, p.441
^John Montague, Basic Perspective Drawing: A Visual Approach, John Wiley & Sons, 2013, ISBN1118414128