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Thanks for the reply, Does this mean REFMAC/Coot does need the missing number flags (and thus you will get improved maps ONLY if uniqueify is run) or does REFMAC/Coot recognise when a reflection is missing and use DFc regardless (in which case there is no point running uniqueify)? Simon On 12 Mar 2008, at 16:00, George M. Sheldrick wrote: > All these programs only refine against reflections that were actually > measured. REFMAC, but not SHELXL, provides the 'Sigma-A' weight > coefficients for Coot to use DFc instead of 2mFo-DFc for the > reflections > for which Fo is not known (or is reserved for the free R) to > calculate a > map. This will in general improve the appearence of the map at the > cost > of introducing a little model bias. As far as I know these > 'unobserved' > reflections are not used in calculating the difference map. CNS is > probably like SHELXL, I'm not sure what phenix.refine does. > > George > > Prof. George M. Sheldrick FRS > Dept. Structural Chemistry, > University of Goettingen, > Tammannstr. 4, > D37077 Goettingen, Germany > Tel. +49-551-39-3021 or -3068 > Fax. +49-551-39-2582 > > > On Wed, 12 Mar 2008, Simon Kolstoe wrote: > >> Dear CCP4bb, >> >> I was looking through the REFMAC manual today and found the >> following advice: >> >> "Completing the data to include all possible hkls. Should do this >> after data >> reduction, and certainly before using REFMAC. This is now done with >> the >> uniqueify script. It is best done using CCP4i." >> >> http://www.ccp4.ac.uk/dist/html/refmac5/usage/examples.html#exam0 >> >> Is it a good idea to always run uniqueify on data before running >> REFMAC - what >> about other refinement programs such as SHELX, CNS or phenix.refine? >> >> Simon >>