Fifty years ago, RAND Corporation developed the Graphical Input Language software system (GRAIL), a revolutionary interface that let users communicate directly with computers using only a pen and tablet. In a 1966 RAND memorandum, the goal was to investigate methods by which a user may deal directly, naturally, and easily with their problem.

Gabriel Groner created a handwriting recognition program that identified handprinted letters, numbers, punctuation, and geometric figures. Running in real-time on an IBM System/360, it correctly recognized 90% of symbols drawn by first-time users. Groner documented his method in a 1966 RAND memorandum on Real-Time Recognition of Handprinted Text.

Tom Ellis was one of the inventors and project leads for the RAND tablet and GRAIL software system. The 10.24" × 10.24" tablet had a resolution of 100 lines per inch, capable of digitizing over one million discrete pen positions. The stylus position was reported every 4 milliseconds as (x, y) coordinates.

The active essay revisits Groner's contribution, providing interactive implementations of his algorithms. All source code is available on Github. You can explore a virtual tablet simulation and see how Groner's smoothing techniques reduced noise from the tablet's discrete grid reporting.