I've had the chance to do a few comparisons between my SD and new Freestyle Lite now. In every case so far the SD has come out higher, always being at least 0.5 above the Freestyle.
Of the tests this morning for example, my fasting was 4.8 with Freestyle, 5.4 with SD.
40 minutes after a breakfast of a fillet of fish, fried onions and cannellini beans with chopped tomatoes (36g protein, 31g carb, 5g fat), the Freestyle gave 6.1, but the SD gave readings of 7.7 and 7.8.
After 1 hour the Freestyle gave 4.8 and the SD 5.4.
Obviously the 1 hour readings are fine either way, but the SD readings at 40 minutes do seem rather high considering the meal I had (relatively few and low GI carbs), and the Freestyle reading seems far more reasonable. My issue is that I have been growing concerned with the raised fasting levels (on the borderline of IPG diagnostic values) and high peaks I've been getting in recent months after meals that shouldn't really cause spikes, and which also seem counter-intuitive considering the vast improvements in my diet (particularly in terms of fewer refined carbs) and exercise in that time. The disparity between the readings seems to be quite consistent at the lower levels, but then seems to grow quite significantly for postprandial readings.
I'm wondering whether the SD might perhaps be affected by some substance in my blood whose levels have changed as a result of my changing diet for example, or whether the meter has for some reason 'drifted' - such that it still provides 'precise' but not 'accurate' readings.