Real space R factor of electron density for each component,
residue side chain, or main chain.
The real space R factor is calculated by the equation
R_real = [Sumi (|Dobs - Dcal|)]/[Sumi (|Dobs + Dcal|)]
Dobs is the observed electron density,
Dcal is the calculated electron density,
summation is for all the grid points
Ref: Branden, C.I. & Jones, T.A. (1990). Nature, 343, 687-689