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No change in size ,  18:48, 8 September 2015
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By specifying the spacegroup and unitcell, you tell XDS that it should index based on those reflections that match that spacegroup and unitcell. In a sense, you _force_ that spacegroup and cell. This will discard other (spurious?) reflections, and usually leads to a clean list of Bravais lattice possibilities.
 
By specifying the spacegroup and unitcell, you tell XDS that it should index based on those reflections that match that spacegroup and unitcell. In a sense, you _force_ that spacegroup and cell. This will discard other (spurious?) reflections, and usually leads to a clean list of Bravais lattice possibilities.
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If the data reduction fails nevertheless (in terms of bad R-factors and [[CORRECT#An estimate for the overall quality of an experimental setup|ISa]] in the [[CORRECT]] step), then chances are that you specified some parameter wrongly, or not accurate enough (ORGY and ORGY are the most likely candidates), or that the crystal does not match your idea about its spacegroup and unit cell. Actually the latter happens pretty frequently (which is why it is always the safest way to collect 180° of spindle rotation unless you know your crystals very well; this is also a good strategy in other respects).
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If the data reduction fails nevertheless (in terms of bad R-factors and [[CORRECT#An estimate for the overall quality of an experimental setup|ISa]] in the [[CORRECT]] step), then chances are that you specified some parameter wrongly, or not accurate enough (ORGX and ORGY are the most likely candidates), or that the crystal does not match your idea about its spacegroup and unit cell. Actually the latter happens pretty frequently (which is why it is always the safest way to collect 180° of spindle rotation unless you know your crystals very well; this is also a good strategy in other respects).
    
If you tell XDS that you do not to know the spacegroup (SPACE_GROUP_NUMBER= 0), then [[IDXREF]] takes all observed reflections into account. By design, the spacegroup decision is then postponed until the CORRECT step, or rather to a run of [[pointless]] after CORRECT, and it may be not vital to closely inspect IDXREF.LP, because CORRECT.LP has basically the same information, plus more.
 
If you tell XDS that you do not to know the spacegroup (SPACE_GROUP_NUMBER= 0), then [[IDXREF]] takes all observed reflections into account. By design, the spacegroup decision is then postponed until the CORRECT step, or rather to a run of [[pointless]] after CORRECT, and it may be not vital to closely inspect IDXREF.LP, because CORRECT.LP has basically the same information, plus more.
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