My experience suggests that, of all the meters I've tried (Abbott (Freesytle), Bayer (Contour), Roche (AccuChek), Agamatrix (WaveSense)) they are all consistent when my blood glucose is in the range 80-160. Once it gets outside this range all bets are off.
Agamatrix fails, terminally, when presented with blood from cold hands; I abandoned it, it simply didn't work in winter.
Dexcom (CGM) was way out most of the time; it was only good for trends. I sent it back and demanded my money back.
I only really care in the range where the meters I've used are accurate - 80-160. If I'm above 160 mg/dl I'm high and it really doesn't matter how high because I won't be rational until I'm approaching 160 again. When my BS approaches 250 I will do several readings in a row using the same meter (at present a Bayer Contour USB). When I do this I consistently see massive variations between the readings.
I'm guessing that, since you are seeing 40mg/dl differences, your figures are likely to be over 140 a lot of the time. If so I wouldn't worry; the treatment is pretty much the same. You have to be careful not to OD on a correction so if you are correcting from a high reading it can get very difficult.
The correction itself often produces feelings of a *low* blood sugar even though the actual blood sugar is still high; I will get cranky if my blood sugar is falling rapidly, just as though I had a low blood sugar. Still, high is high; the best solution is a gradual return to normal.
John Bowler jbowler at acm.org