**Definition:**

Residual factor R~cullis,ano~ for anomalous reflections for this derivative. The Cullis R factor was originally defined only for centric reflections. It is, however, also a useful statistical measure for anomalous reflections, which is how it is used in this data item. This is tabulated for acentric terms. A value less than 1.0 means there is some contribution to the phasing from the anomalous data. sum |Fph+~obs~Fph-~obs~ - Fh+~calc~ - Fh-~calc~| R~cullis,ano~ = ------------------------------------------------ sum|Fph+~obs~ - Fph-~obs~| Fph+~obs~ = the observed positive Friedel structure-factor amplitude for the derivative Fph-~obs~ = the observed negative Friedel structure-factor amplitude for the derivative Fh+~calc~ = the calculated positive Friedel structure-factor amplitude from the heavy-atom model Fh-~calc~ = the calculated negative Friedel structure-factor amplitude from the heavy-atom model sum is taken over the specified reflections Ref: Cullis, A. F., Muirhead, H., Perutz, M. F., Rossmann, M. G. & North, A. C. T. (1961). Proc. R. Soc. London Ser. A, 265, 15-38.

**Type:** float

**Mandatory item:** no

The permitted range is [0.0, infinity)

**Category:** phasing_MIR_der

Copyright © 2005 International Union of Crystallography