Accuracy, Precision, and Other Balance Limitations

The greater the accuracy of a balance, the closer the balance will read the nominal weight of a calibration weight. If the calibration weight reads 10 mg, the balance should read 10 mg. If, for example, the balance reads 10.5 mg, it has less than desirable accuracy, and if it reads 12 mg, it has poor accuracy. 

Readability refers to the smallest measurement that a balance can indicate and that can be read by an operator when the balance is being used as intended. Generally, triple-beam balances have a readability of 0.1 g, centigram balances have a readability of 0.01 g, and analytical balances have a readability of 0.0001 g. 

The nominal weight of a calibrated mass is the calibration that is printed on, or stamped into, its surface. 

Neglect or abuse can damage a balance resulting in no deflection for the original smallest units. The result is a change in the readability for the damaged balance to a new, and larger, value. 

Off-center errors are problems specifically associated with top-loading balances. Placing a balance pan above the fulcrum places different torques and friction on balance pieces that do not exist when a balance pan hangs. The problem is exhibited if an object has different weight readings when moved to various locations across the surface of a top-loading balance pan. 

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