static char sccsid[] = "@(#)pic.1 1.3 (CWI) 87/04/30";
pic - troff preprocessor for drawing simple pictures pic [ -T t ] [ files ] Pic is a ditroff (1) preprocessor for drawing simple figures on a typesetter. The basic objects are box , line , arrow , circle , ellipse , arc and text.

The optional argument -T t specifies typesetter t ; currently supported typesetters are har (Harris 7400, the default), 202 (Mergenthaler Linotron 202) cat (Graphic Systems CAT), and aps (Autologic APS-5).

ditroff(1), dieqn(1)

B. W. Kernighan, "PIC \(em A Graphics Language for Typesetting"

The optional argument -D specifies that all lines are made with the drawing functions \eD'...' of ditroff (1). This wil make a nicer picture, but creates much more date and is more time consuming. Without this argument, some horizontal and vertical lines won't match nicely. You're advised not to use this argument at trial runs.