Although most of our scales come pre-calibrated, it is always good to be able to verify that your scale is weighing correctly. Weather your scales is knocked around during shipping, or is dropped at home and hits the floor, scales can become uncalibrated fairly easily. With a calibration weight you will just need to enter your scale's calibration mode (see instruction manual) and re-calibrate to make sure it's doing it's job perfectly. Available in several weights. All scales vary on which needs to be used in calibration mode. Please refer to your scale's instruction manual to determine what weight you need.