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Dear Crystallographers, There have been comprehensive discussions on the use of criteria such as Rmerge and I/sigma(I) as criteria to define the resolution to which X-ray data is to be used for structure determination. However, CC 1/2, the correlation between random half sets of data, is increasingly being considered as a better means for evaluating the resolution cutoff (Karplus and Diederichs). Is there a resolution cutoff that can be considered as a acceptable standard, say CC 1/2 = 0.5, or does this prompt the counter-question 'how long is a piece of string?' in which case resolution values are to be quoted at CC 1/2 values of 0.2, 0.3, 0.5, 1, etc? Best wishes, Michael Michael Roberts Crysalin Limited Cherwell Innovation Centre 77 Heyford Park Upper Hey ford Oxfordshire OX25 5HD