Houston Instruments HIPAD Digitizer

The HIPAD did not begin as a desktop accessory. Håkan Lans's brief was a control device for digitizing seismic measurements: a paper record or map was clipped to a drafting table and the operator marked measurement points with crosshairs. In that context the tablet was an instrument for turning a physical document into numbers, and the crosshair puck — not a mouse — was the natural sensor. The interaction was deliberately direct: look through the crosshair, align it with a feature on the paper, press a button to commit the sample. It is a workflow inherited from cartography and exploration geophysics, where the document is the data source and the machine's job is to capture it faithfully.

The engineering problem was drift and lost orientation. Earlier digitizers required a known origin and lost their sense of place when the pointer was lifted. Lans's solution encoded position absolutely on the surface: loops in four separate layers carried different frequencies, the inductive pointer picked each up, and the phase shift across the loops gave the pointer's location. Because position is encoded in the surface rather than accumulated from motion, the puck can be lifted, a document slid underneath, and coordinates remain correct. The advertised precision, about 1/10 mm, was fine enough that the operator's ability to place a crosshair — not the electronics — was the limiting factor. This absolute-versus-relative contrast is the one that later became central to graphics tablets, pen displays, and touch input; here it is present in a 1970s instrument.

The museum's HIPAD puck has four labelled buttons: RESET, POINT, SWITCH STREAM and STREAM — a vocabulary belonging to a streamed coordinate protocol rather than to mouse clicks. The labels distinguish a single committed "point" from a "stream" of positions, with a switch to toggle streaming and a reset to re-originate. The exact host commands lie in period driver documentation rather than in the object itself, but the names alone show a device whose output is a flow of numbers the host must interpret. The crosshair made tracing and point-picking over a paper document a glance-and-press operation, and the mode buttons let the operator choose between sampling a single feature and dragging a continuous trace.

The HIPAD is also a story about the moment personal computing created demand for pointing devices. According to the Tekniska Museet record of Lans's account, after two years Houston Instrument wanted to stop production because they had made only about 70 units; Lans persuaded them to continue because he believed the personal computer would create a need for pointing devices. Shortly afterwards demand rose dramatically, and Lans estimated that 10,000 units were being manufactured a month. Whether or not that estimate is exact, it records the pivot from a niche digitizer for surveyors to a mass-market peripheral in the early 1980s — one of the clearest cases in the collection where a professional instrument's sensing technology crossed over into everyday computing.

DECUS reporting from October 1979 places HIPAD support on DEC's MINC laboratory computer, so the tablet was in scientific laboratory use, not only drafting. The same absolute-positioning property that made it useful for tracing maps and seismic charts made it useful wherever a paper document had to be digitised exactly: cartography, geological survey, PCB layout, and eventually CAD. A large absolute surface with a crosshair puck and mode buttons was a natural front end for the workstations of the late 1970s.

The museum's Summagraphics Bit Pad entry covers the magnetostrictive line; the HIPAD covers the inductive, absolute line, and adds an outsider's story: a device born in geophysical survey work, engineered by a Swedish inventor, commercialised by a Texas instrument maker, adopted in labs and drawing offices. It reminds us that "point and click" was for years only one pointing idiom, and that the absolute tablet — where surface and document are the same — was the professional's alternative. Its physical details are unusually legible: crosshairs, a four-button puck, a gridded translucent surface, and a D-sub connector are exactly the hardware a digital museum can preserve and explain.