Tuning is the process of determining what corrections must be made to the model input parameters for a particular point to make it exactly match the Base assay value. It is performed for each point of the Base assay, and the results are both a measure of the uniqueness of the crude, and, potentially, an indication of an error in the Base assay. The tuning factors are assumed to apply to the new assay, and can be interpolated to give values for new cut points (re-cutting).

The Tuning includes 2 portions; 1) factors related to whole crude properties, 2) remaining errors.

The tuning factor ralated to Whole Crude properties is the HPI_K (Characterization Factor) correction. The K is a measure of aromaticity and many properties are sensitive to this property. The tuning process finds a K factor, within the normal range of Ks, that makes the prediction match the Base. If the K tries to move outside of the normal range, or if the property is not sensitive to K, an offset correction is calculated. For most properties this is an absolute difference (Actual-Predicted), but some property accuracies are determined on a relative basis and the offset is a multiplier (Predicted/Actual).

The Tuning is controlled by a "Tuning Control" of the form "0.5 K". This indicates that the HPI_K factor can be adjusted up or down 0.5 K from the Base assay value. If the property is not responsive to K the equation would be "0.0 K". The result of the Tuning is retained as a "Tuning Equation" of the form "0.043 K + 3.3 Offset" or "0.0 K + 0.978 Mult". This indicates the amount of K correction and Offset or Multiplier needed to make the model exactly match the Base assay data.

Since the CCPP models contain the relationship between cut points and property values, these Tuning factors can be interpolated to new cut points, based on average boiling points. This allows crudes to be recut or for predicted assay cut points to be different from the Base.