The isomorphous Hendrickson-Lattman coefficient A~iso~ for this reflection for this derivative. -2.0 * (Fp~obs~^2^ + Fh~calc~^2^ - Fph~obs~^2^) * Fp~obs~ * cos(alphah~calc~) A~iso~ = ----------------------------------------------- E^2^ E = (Fph~obs~ - Fp~obs~ - Fh~calc~)^2^ for centric reflections = [(Fph~obs~ - Fp~obs~) * 2^1/2^ - Fh~calc~]^2^ for acentric reflections Fp~obs~ = the observed structure factor amplitude of the native Fph~obs~ = the observed structure factor amplitude of the derivative Fh~calc~ = the calculated structure factor amplitude from the heavy atom model alphah~calc~ = the calculated phase from the heavy atom model