Hi all, I've just realised that the mmCIF provides no formal specification of the conversion factor between B's and U's. If a program module looks for _atom_site.B_iso_or_equiv, say, and it is absent, it can determine from the ITEM_RELATED DDL category that it is related to _atom_site.U_iso_or_equiv by a constant, but has no way of determining what that constant is. In all the time that I have been looking at the dictionary, I had just assumed that when I got around to it, I would be able to write a routine that would return a B-value, when a U is present in the CIF, and that I wouldn't have to hard-code crystallographic knowledge into my software. Just goes to show how important it is to check everything..... The only way around this, without changing the DDL, is to specify different unit names for B's and U's, and give the conversion factor in the ITEM_UNIS_CONVERSION category. Cheers, Peter. ======================================================================== Peter Keller. \ "We kill the cows to make jackets out of Dept. of Biology and \ them, and then we kill each other for the Biochemistry, \ jackets we made out of the cows." University of Bath, \ --- Denis Leary Bath, BA2 7AY, UK. \ ------------------------------\----------------------------------------- Tel. (+44/0)1225 826826 x 4302 | Email: P.A.Keller@bath.ac.uk (Internet) Fax. (+44/0)1225 826449 | P.A.Keller%bath.ac.uk@UKACRL (BITNET) ========================================================================