| You couldn't be further from the truth, there are sooo many variables it's amazing they can give a reasonably accurate result. Further to what's already been suggested anything you touched recently from bacteria to soap can have an effect and let's not forget sudden fluctuations that will take time to circulate round the body. Then the human body is more complicated that the scientists understand swings in bgs can be caused by hundreds of reasons. Sadly the meter inaccuracy is the price we pay for size and speed; there are bigger heavier slower meters that are very accurate but you can't fit it in your pocket or bag (easily).
The next argument is why don't they make meters more accurate that could fit in your pocket, the answer is that they are accurate enough to enable a decision on treatment to be made. More accuracy wouldn't necessarily give you a major advantage. For example difference between knowing that my actual bg is 52 (2.9) or with meter error 60 (3.3) or 44 (2.5) is little as I would still treat with the same number of carbs. This game is full of numbers none of which are as accurate as a human pancreas and because of this we simply have to do the best we can at utilising the tools we have today. | 
