In the Computer History Museum video celebrating the PDP-1 restoration, there is a mention of T-Square possibly being the "first electronic drafting" program, and that it used the Spacewar! controllers. Spacewar! apparently first ran in February 1962. In his MIT PhD thesis published in 1963, Ivan Sutherland explains he completed an early version of Sketchpad that could draw parallel and perpendicular lines in November 1961. Sutherland goes on to say, "Somewhat before my first effort was working, Welden Clark of Bolt, Beranek and Newman..." showed him a "similar program" running on a PDP-1. It would be interesting to know what program that was.