Electronic balances must be calibrated with a mass standard upon installation and on a regular basis thereafter. Calibration values vary over time because of changing conditions within the balance or its environment, such as movement or relocation of the balance, differing gravitational forces, temperature variations and aging electronic components.

Which Class is Right for My Application?
A balance should be calibrated using a weight with a class tolerance factor greater than the readability of the balance. Example: A toploading balance with readability of 0.01g may be calibrated with a weight having a known tolerance of at least 0.009g.