F1CHF, The probable reason for the A/D reading jumping around is the input has some noise on it and it is being digitized. With a 5 volt reference for the A/D the minimum resolution per bit is 4.9 Millivolts. You should either do some kind of analog filtering using an RC network or do some kind of software filtering. The A/D is only telling you what it sees. Also make sure you have a ROCK stable reference voltage at the PIC. If you have access to a scope, use it, you will be supprised at what you see...

Dave Purola,
N8NTA