If the scale displays "CAL" it needs to be re-calibrated. The following instructions can be found in the owner’s manual:
Calibration
While the scale is off, press ON/OFF button to turn on the scale > the LCD will read "0.0g".
• Press and hold the MODE button until the display shows "CAL", then release the button.
• Press MODE button again, > "500g" will flash on the display.
• Place a 500g calibration weight onto the center of the platform.
• The LCD will read “PASS” then return to the normal weighing mode.
• Calibration is complete.