Whitcombe et al (2002) give the scaled reflectivity related to an EEI log at a given Chi as

Where A and B are the AVO intercept and gradient from the commonly used 2-term Zoeppritz linearisation given as

Setting Rs = 0 gives the following relation

where Chi0 is the Chi angle at which the reflectivity, as defined by the conventional 2-term AVO equation, is zero. We refer to this Chi angle as the "minimum energy Chi".