You honestly cannot expect too much when using the supply for the reference.
This method works fairly well for ratiometric ideas, such as strain gauges or
temperature resistor dividers.  STRONGLY suggest a reference of some fashion.
Remember to check PPM temperature drift too.  You anly need 8 bit res, so it
shouldn't be too bad to get 1/256 PPM or better.  Last but not least, decouple
your supply to the PIC reeely well.  I used the 0.1 and a 470Uf on that end of
the board.  That 470 solved my one bit flicker.  G'luck.

Chris Eddy
Pioneer Microsystems, Inc.

Gordon Zerf wrote:

> I am using a 16C71 as a 4 channel voltmeter, but find that the last digit
> fluctuates so much that it is a problem. I am using internal referance and
> have measured the supply etc. and everything is stable. How do I solve this
> problem ?
>
> Gordon