• If you have two spectra to assign to two possible compounds (one way round or the other) we recommend using the CP3 parameter. CP3 requires calculated and experimental shifts for two compounds.
• If you have one spectrum to assign to one of many possible compounds we recommend using the DP4 parameter. DP4 requires the experimental shifts for the compound being assigned and calculated shifts for each of the possible candidate structures.

Assigning the Stereochemistry of Pairs of Diastereoisomers Using GIAO NMR Shift Calculation
S. G. Smith and J. M. Goodman J. Org. Chem. 2009, 74, 4597-4607
DOI: 10.1021/jo900408d

Assigning Stereochemistry to Single Diastereoisomers by GIAO NMR Calculation: The DP4 Probability
S. G. Smith and J. M. Goodman J. Am. Chem. Soc 2010, Accepted
DOI: 10.1021/ja105035r