> > For example for space group no 18 with the 'short' H-M symbol 'P 2/1 2/1 > > 2' in the setting with 'full' H-M symbol 'P 2 2/1 2/1' the programs > > choose the correct conventional cell as say a=60, b=70, c=90 > > (according to the convention a<=b<=c).
The convention is a<b<c for P212121 and P222 I think. If you have (60 70 80 90 90 90) P 2 21 21 I think the reference setting (using cctbx/sginfo terminology) you are looking for is (70 80 60 90 90 90) P 21 21 2. If you have data in any weerd setting, using iotbx.reflection_file_converter mydata.sca --change_basis=to_reference_setting --sca=reindexed.sca should get you back to the reference setting. Not sure about ccp4 programs, but programs based on the cctbx symmetry libraries, should be able to handle data in unusual settings, which is usefull in some situtaions. HTH Peter
