What is calibration?
Calibration simply means that you are teaching the scale what ZERO weight is and another known ACCURATE or "span" weight.

Why is it important to have an accurate weight for calibration?
Since you are teaching the scale a known weight, it is important to make sure the weight applied is as accurate as possible. Most scales allow you to choose what weight you are using for calibration, they are typically 10%, 25%, 50% of the scales capacity. Once defining your calibration weight, and performing a calibration, the scale will mathmetically calculate the weight placed on the scale above the calibration weight used. Using an inaccurate weight will cause your scale to weigh inaccurately every time.

When does a scale require calibration?
Most companies have a calibration policy to comply with their ISO or Qaulity System Procedures. Scale manufactureres typically recommend a yearly calibration to ensure accurate weighing. Scales can loose their accuracy or intial calibration values from being shipped by the manufacturer, a significant change in altitude, numerous overloads or underloads, or deflections accuring from the mechnical structure not being aligned properly.

Is calibration covered under warranty?
Typically calibration of a scale is not covered under warranty. Calibration is not defined as a product defect. Some companies will allow your scale to be returned to the factory for a minimal fee. A certified scale technician, found in your local yellow pages, is the recommended method for installing a new scale or performing a annual calibratrion.