> No, if the next sample is a complete random value.

This is correct... The example I read (in the manual for the 16F630)
shows that the hold capacitor charging/decharging is the largest part
of the time. However, it also talks about the maximum allowed error.

This all brings me to another point, which is the actual LCD display.
When I read the original question, I was thinking of the usual type of
display I would attach to a PICmicro. Obviously it would need to be
graphical, so a T6963C of 64*128 ($25 on futurlec) pixels seemed like
an appropriate choice. Obviously you can go more expensive, but at
some point a dedicated external A/D converter would become preferable
(as the price/size of the display would outweigh the cost/size of the
A/D converter).

Given a 64*128 bit display you only need 128 samples, and not 500.
Also, you only need 6-7 bits of resolution, which means you can skimp
on the acquisition time (note that the 10F220 manual, with its 8-bit
A/D converter, doesn't even mention acquisition times, and assumes all
conversions can take place within 7us).

Greetings,
Maarten Hofman.

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