The act of calibration standardizes a model. Many models are developed for specific situations and are, by definition, calibrated to that situation. Such models usually are not useful outside of their particular environment. The act of calibration is needed to increase the accuracy of one of these general models by making it temporarily a specific model for whatever product it has been calibrated for.
Calibration is in a sense customizing a generic model.
Calibration is the process of determining the deviation from a standard in order to compute the correction factors. For cost estimating models, the standard is considered historical actual costs. The calibration procedure is theoretically very simple. These estimates are then compared with the actual costs and the average deviation becomes a correction factor for the model. In essence, the calibration factor obtained is really good only for the type of inputs that were used in the calibration runs.