Hi! IIRC, the spin number is set according to information in the read pdb file. So the @N of residue number 2 can have e.g. the spin number 18, and so on. Where exactly does this number come from? And is there a way to rename the spin_num to a value that corresponds e.g. to the res_num? To me it seems more convenient to assign the same number to both spins and residues, as every residue has only one backbone-N. With the somewhat arbitrary spin number it's quite complicated to import external R1, R2 relaxation fits that do not take any spin information from a pdb file into account. (I have a bunch of files I created for TENSOR and these do only contain residue numbers.) Any hints how to change that would be appreciated. I have no experience in Python but have no problem to learn. Cheers Martin -- Martin Ballaschk AG Schmieder Leibniz-Institut für Molekulare Pharmakologie Robert-Rössle-Str. 10 13125 Berlin ballaschk@xxxxxxxxxxxxx Tel.: +49-30-94793-234/315 Büro: A 1.26 Labor: C 1.10