[ccp4bb]: about REFMAC5

[GUAN <grj@pewdc.ibp.ac.cn>]

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I use CNS to refine a structure to R=16.99% and Rf=18.92% with
a 1.4 A data set, and use REFMAC5 to refine anisotropic B factors,
as suggested by many experts on CCP4 BB. The result showed a R
of 13.11% and Rf of 16.50%.
But an expert here said that the number of my reflections is not
enough for this refinement, so the result was some meaningless.
I have 19255 reflections, 132 residues and 146 waters in the A.U.,
(total 1154 atoms). Each atom has 9 parameters to be refined
(3 coordinate parameters and 6 anisotropic B factor parameters),
so the ratio of reflection over parameters is about 2, not very
high.
so, I wonder when to refine anisotropic B factors using REFMAC5?
what should the ratio should  be? How to tell the if the result 
is OK or meaningless?

Thanks,
Rong-Jin Guan