Yup... SICK is the manufacturer and the NT6 is an optical sensor that views colours in greyscale, rather like a black and white photo. Wobble is the inconsistent readings I'm getting which are in the region of ± 1 (56..58 out of the 1024 10-bit range). Actually it is not known whether this is ±1, +2 -0 or +0 -2...and so whether additional wander is possible at the wave of a hand (not a metaphor) I can't say. Neither can I say whether the mean value can change easily or what can (or perhaps what can't) make it change.
I'd really like to constrain this further because I would feel like I'm cheating to 'program' around it. Perhaps an experiment with a battery will at least give me experience in this matter and I have to say, the idea of noise originating from processor activity makes me think this analogue business might be an art (based on science obviously!).
Thanks for the advice.