The PV-650 digital pocket scale features a stylish, round back-lit LCD display. Always fits easily in your pocket or handbag for weighing on the move. The removable hard plastic cover protects the scale when it's not being used and doubles as an expansion tray. In most cases this scale will arrive in perfect calibration, which are pre-calibrated from manufacture. Scales that weigh in 0.1g or smaller increments will need to be calibrated from time to time. Many things can effect a scales calibration including but not limited to: shipping, humidity and general use. Please remove clear protective cover from weighing surface before you weigh items.