A balance scale measures weight by comparing the unknown weight on one side of a lever to a known weight on the other side. The scale at the doctor's office is a physician's balance scale, and a scale commonly found in a high school chemistry lab is a triple beam balance scale. Both use the principles of balancing a known and an unknown weight across a lever to determine gravitational mass or weight. Although these scales are usually calibrated at the factory and are very accurate, moving the scales, heavy usage and environmental factors such as temperature and humidity may cause them to go out of calibration, resulting in inaccurate weights. Test and calibrate your balance scale regularly to maintain accuracy.
Manual Balance Scales
Zero the balance by sliding all of the weights to zero and leaving the platform empty. If the pointer is not on zero, turn the balance adjustment screw or zero adjustment knob until the balance reads zero or indicates a balanced position.
Place a known weight such as a dumbbell or barbell weight on the platform. Adjust the weights until the scale reads a balanced position. Compare the known weight of the dumbbell to the weight indicated by the scale. For example, if the dumbbell is 12 lbs. but the scale weighs it as 14 lbs., the scale needs to be calibrated down 2 lbs.
Adjust the lever arm according to the calibration change desired.
Electronic Balance Scales
Turn the scale on and zero the scale prior to calibration.
Set the scale on calibration mode. Enter load weight.
Place the dumbbell on the platform and allow the scale to calculate the weight. Remove the weight as the display indicates. Press "Enter."
Allow the scale to re-calibrate itself based on the comparison of the weight you programmed into the scale and the weight of the dumbbell that the scale registered. Do not move or shake the scale or place anything on the platform.
Replace the weight on the platform as the display indicates. Press "Enter." Remove the weight when the display indicates that the scale is done re-calibrating.