[ccp4bb]: Unit Cell Parameters

[Alessio Accardi]

Hi all,

I am very sorry if I have a somewhat trivial question, but I am quite new to the crystallography world.
I process my data with Denzo followed by Scalepack and I noticed that  the unit cell parameters in the scalepack .log file and in the final output *.sca file are different; not by much, at most around 1-1.5%.

This is the readout from the middle of the scalepack.log file:

 Hkl's refined: 379123 N.Chi**2:    1.227 Decrease:   0.000 * 379123 =      0.5
 Film #       a       b       c   alpha    beta   gamma    crysz    crysy    crysx mosaicity
      1 232.332  97.983 170.963  90.000 131.210  90.000   75.087   18.917  135.045   1.082
      2 232.332  97.983 170.963  90.000 131.210  90.000   75.126   18.942  135.056   1.082
      3 232.332  97.983 170.963  90.000 131.210  90.000   75.124   18.933  135.057   1.082
      4 232.332  97.983 170.963  90.000 131.210  90.000   75.126   18.930  135.056   1.082
      5 232.332  97.983 170.963  90.000 131.210  90.000   75.117   18.908  135.052   1.082

And this is the readout from the top of the output.sca file:

230.822    97.684   170.202    90.000   131.114    90.000 c2      

First of all which of the two sets of values is the correct one to use in refinement? I would guess that the right one is the one in the .sca file as the hkl's and intensities refer to that unit cell, but I am not sure. Also, why are the values different? do they reflect different stages of refinement of the processed data? if so, is the one in the .sca file the more refined one?


Thank you

Alessio
Brandeis University