if you were due to test half hour later, i would think the initial readings were as your levels were climbing. i'm guessing you were testing just after a meal (half hour after maybe) - the level you had to take at one hour after a meal is the one that is most significant as that is when your BSL's will peak. (hope that makes sense). if you tested over 10minutes for the other tests, it's likely you were actually watching your BSL's climb

as trillian said, make sure your hands are clean and dry when you test as things like water/sweat on your hands can change the reading.