<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hi George,<div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>My non-mass-weighted script should have been dividing by the number of atoms and it wasn’t. I’ve attached a corrected version. Nonetheless, the Amber calculation is using mass weighting, so that is not the issue. I need to emphasize again that the script is going to compute the radius of gyration of all atoms in your model, regardless of which ones are selected. The only way to compute the value (with that script) for a subset of atoms is to delete all the other ones. For instance, with the PDB you sent if I delete all atoms except for residue 26, this is the output I get using the mass-weighted script:</div><div class=""><br class=""></div><div class="">#0 center of mass: 26.1014 36.0445 34.9565, radius of gyration: 1.934</div><div class=""><br class=""></div><div class="">If you want the script to work on the currently selected atoms instead of all atoms, I could send you a modified script that does that. Let me know if you want that.</div><div class=""><br class=""></div><div class="">—Eric</div><div class=""><br class=""></div><div class=""></div></body></html>