- …digitiser.
- This was a digitiser in which the tip
of the pen contained a small spark gap. Several times a second, a
spark would be triggered which made a little “tick.” The digitiser
measured the time the sound arrived at two microphones and, knowing
the speed of sound, calculated the position of the pen. AutoCAD
supported two models, the 18×24 inch GP-7 and the
60×72 inch GP-8. A 3D model was also available. The sparks created
ozone, which contributed to the electric feeling of pioneering
desktop CAD. The pen was also handy for chasing away pesky cats.