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CORRECT is the scaling step of XDS. | CORRECT is the scaling step of XDS. | ||
== | ==An estimate for the overall quality of an experimental setup== | ||
A useful Unix command | A useful Unix command that prints a single number that depends on the overall quality of an experimental setup (beam, crystal, spindle, detector, cryo, software, ...) is | ||
awk '/CORRECTION PARAMETERS/{for (i=0;i<9;++i) getline;print 1/($1*$2)^0.5}' CORRECT.LP | awk '/CORRECTION PARAMETERS/{for (i=0;i<9;++i) getline;print 1/($1*$2)^0.5}' CORRECT.LP | ||
Why? Because this will give you the best (maximum) value of I/sigma(I) for any reflection in your dataset - even if your crystal is great, all reflections are bound to be worse than that. | Why? Because this will give you the best (maximum) value of I/sigma(I) for any reflection in your dataset - even if your crystal is great, all reflections are bound to be worse than that. | ||
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If your crystal is badly split or broken, then of course a and b will be strongly influenced by the crystal quality. If your data reduction is not good (e.g. wrong spacegroup) then the values of a and b might not be reliable. | If your crystal is badly split or broken, then of course a and b will be strongly influenced by the crystal quality. If your data reduction is not good (e.g. wrong spacegroup) then the values of a and b might not be reliable. | ||
If your crystal is good (and no matter how good your crystal is!), then a and b will reflect the quality of the beamline. I have seen values lower than 20 for good crystals at bad beamlines. On the bright side, I have also seen a value of 87 for Z. Dauter's 0.98A Proteinase K sulfur-SAD data from J. Holton's APS/22-ID beamline. | If your crystal is good (and no matter how good your crystal is!), then a and b will reflect the quality of the beamline. I have seen values lower than 20 for good crystals at bad beamlines. On the bright side, I have also seen a value of 87.6 for Z. Dauter's 0.98A Proteinase K (2ID8) sulfur-SAD data from J. Holton's APS/22-ID beamline. | ||