Hello, I am working with chimera sessions involving a large numer of 70S ribosomes. I keep modifying the sessions over and over, so I save new sessions every day. Much of what I do is labeling interesting residues, measuring distances, coloring these residues, etc. Sometimes I make a mistake, like accidentally selecting and modifying a large portion of the model, and I loose an important amount of information. In these cases, I find that there is no way to go back to the previous state of the system, other than clossing the session and re-opening the latest saved one. Unfortunately, this means loosing a lot of unsaved work. While there is an "undo" option under the "select" tab, it does not really allow one to return to the previous state of the system. In fact, I'm not even sure of what it does. My question is, is there a way to return Chimera to the state ocurring immediately before the last action? In case this does not exist, can it be implemented? best, Antón -- Antón Vila-Sanjurjo, PhD Marie Curie fellow Grupo QOSBIOS, Dept. Química Fundamental Facultade de Ciencias Universidade de A Coruña (UDC) Campus Zapateira, s/n 15.071 - A Coruña - España (Spain). tlf: (34) 981-167000 ext:2659 e-mail: antonvila.s@gmail.com