It's the little things that can really foul us up in our day to day diabetes self-care. Case in point: simply cleaning hands before a BG check. I DID NOT clean my hands when I got the first value of 170 mg/dl [9.4 mmol/L]. I noticed a significant variance compared to my CGM device (lower).
Of course I then washed my hands and rechecked. Voila, 102 mg/dl [5.7 mmol/L]. It was a much more "in range" value and consistent with my CGM device at that moment in time.
Now think about this. What if I DIDN'T have a CGM to compare with? What if you are a d-kid (or adult) and take any meter value you get at face value? Imagine if you chose to dose rapid acting insulin to lower the higher BG value, when in reality you were much lower? It would imply that insulin works faster than you were taught, or that low BG symptoms could happen at "higher" values than you were taught. Get the point?
This is another potential reason why strange and at times unexplained results occur in diabetes. Our diabetes devices are hardly foolproof and prone to a certain amount of user error, even under ideal conditions. And even when user error is taken into account, these devices themselves have an error rate. This is well known but not always very appreciated as much as it should be. Imagine the "non ideal" BG testing conditions which define almost all of our daily lives with diabetes.
This is also another reason our diabetes can often seem chaotic. And for the record I did check a 3rd reading: 104 mg/dl. Good critical thinking is a valuable diabetes self care skill.
Food for thought...