There is not much you can do to calibrate a syrup hydrometer. There are times when the paper slips down the tube and would give an inaccurate reading. The Smoky Lake Maple syrup hydrometer has marked where the paper should be so that you know if the paper has slipped. Once again though, this will only indicate that there has been damage to your hydrometer and that it should be replaced. You could also compare one hydrometer reading to another if you suspect one is inaccurate.