They are very accurate for the price. just sensitive and have to be used on a level surface. One trick is to remember the exact weight of your tray right before you check the calibration weight. Your tray should weigh exactly the same thing every time. The correct weight will be whatever it is right before you get a perfect 10.000 with the calibration weight. If the tray is something different you know your powder weight is inaccurate.
Mg calibration weights are also nice to have: