Source : Free On-Line Dictionary of Computing

Sketchpad
     
        A program that allowed users to draw on a screen with a {light
        pen}.  It supported constraints (e.g. drawing a constrained
        ellipse produced a circle).  It also had some {computer aided
        design} features (e.g. computing loads on beams).
     
        Sketchpad was the subject of {Ivan E. Sutherland}'s 1963 {MIT}
        PhD thesis, which opened the field of {computer graphics}.  It
        was the progenitor of computer drawing packages like {MacDraw}
        or {Adobe Illustrator}.  There is a film of Sketchpad in
        action.
     
        It solved {constraint}s using {value inference} and introduced
        the "{ring}" list structure.
     
        ["Sketchpad: A Man-Machine Graphical Communication System",
        I.e. Sutherland, MIT Lincoln Lab, TR 296 (Jan 1963)].
     
        [Sammet 1969, p. 678].
     
        (1995-02-14)