[NTLK] Why are pen alignments needed?

Terence Griffin griffin at nist.gov
Thu Dec 6 13:36:59 EST 2018

A resistive touch sensor is separate from the display. Perfect alignment 
during assembly of the device is non-trivial. And because they're 
thicker and stand off from the display, there is parallax. How you hold 
the device effects the location of the touch points. Capacitive sensors 
are integrated into the display. The sensor layer is attached to the 
display when the display is manufactured, as opposed when the device is 
being assembled. One of my Palm Pilots had a nonlinear error. If I 
carefully tapped the exact location for each calibration point, it would 
be out of alignment on some portion of the screen. I think in the UR 
corner, the touch points were stretched outward. I had to "lie" to get a 
usable calibration. I never discovered what was causing the error. 
Finally, if the display or touch sensor needs to be replaced, 
calibration will almost certainly be necessary.

I had a comp sci prof who talked about v-hold knobs in software. In the 
days of analog TVs, oscillators that were accurate and precise for the 
lifetime of the TV were very expensive. So the cheap fix was to have 
adjustment knob to fix things when the oscillator drifted: the vertical 
and horizontal hold knobs. To keep costs down, they used the cheapest 
knobs they cold fine. Since they were not pretty, and were (hopefully) 
used infrequently, they were put on the back of the TV. So the v-hold 
was a quick and dirty out for a difficult engineering problem. The 
lesson was we should design our software to avoid needing v-hold knobs. 
Touchscreen calibration maybe a v-hold knob.

- Tere

On 12/05/2018 01:56 PM, B Dudney wrote:
> The true techies on this list know more about, but my understanding is the software is somewhat sensitive to how one holds the stylus, plus maybe it couldn’t adjust itself when one changed screen orientation.
> It’s very early HWR system; better than Model T, but not a Ferrari.
> B
> Doug wrote:
>> can someone explain why pen alignments were necessary on the Newton?
> via cable from low-power MacBook lacking wireless devices,
> hence radiating no deadly EMR connectivity: see RadiateNot.Me;
> plus powered by non-radiating coaxial DC cable from utility shed
> where wall wart* EMR is indetectably far away
>                             *standard Apple shielded power supply = less emissions
> ----------------------------------------------------------------------
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