The resistance of the potentiometers should be a linear taper. Based on
the design of the integrating analog-to-digital converter used, the
maximum resistance should be no more than 528K (470K +/- 10 percent is
suggested) for either the X or Y pots. This is based on a charge capacitor
of 0.047uf, +/- 10 percent, and a maximum time of 16.6 milliseconds for
charge to full value, ie. one video frame time.

All potentiometers exhibit a certain amount of "jitter". For acceptable
results on a wide base of configurations, several input readings will need
to be averaged.

     figure 8-6: potentiometer charging circuit