3838212 is referenced by 40 patents and cites 6 patents.

A graphical data device employing a stylus moving over an area to be digitized and utilizing a fast rise time sound energy shock wave, generated by a spark at the location of the stylus and propagated through the air for providing coordinate information as to the instantaneous position of the spark. Receiver devices are positioned along X and Y coordinates and respond to the leading edge of the air propagated shock wave front to provide an elapsed time indication from the moment of spark generation to the moment of shock wave reception. In a further embodiment, a three dimensional configuration is employed, utilizing a three coordinate receiver.

Title
Graphical data device
Application Number
04/841,058
Publication Number
3838212
Application Date
July 11, 1969
Publication Date
September 24, 1974
Inventor
Phillips Stanley C
Banks William
Fine Samuel
Whetstone Albert L
Assignee
Amperex Electronic Corporation
IPC
G08c 21/00
G06F 03/33
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