I have 3 identical glucose monitors. I keep one at home, one at work, and one in the car. Yesterday I decided to test with all 3 to see how closely they would read. Within less than a minute, the first said 167, the second said 79, and the third was 109. This was after testing all 3, each with the test fluid that came in the box with it. How are you supposed to know which (or if) one is right?