I'm trying to write a script to be used in the per-frame operation of chimera MD Movie (I'm not an accomplished python programmer). The script I wrote calculates order parameters and internal relaxation elements. It appears that I have to import some chimera commands as well as the python math library to do this. Everything works on a single frame, but I need to pass some variables from frame to frame, and the import commands appear to reset all variables at each new frame. Is there a way to set some global variables or to do the imports only once outside the pre-frame script? Jim James H. Prestegard Professor and GRA Eminent Scholar, Emeritus Complex Carbohydrate Research Center University of Georgia Athens, Georgia, 30602, USA 706-542-6281