Hi Jeff, Chimera does not know what units you are using, the data coordinates are just numbers as far as it is concerned. If you open a PDB atomic model the coordinates are always Angstroms. If you open a density map, say an MRC file, the header may include the voxel size. That value could be in Angstroms or nanometers. Often maps don't have the true voxel size in the header, often they say it is 1. In such cases you can use the Chimera volume dialog menu entry "Features / Origin and Scale" to set the voxel size in Angstroms or nanometers so that the map can be aligned with other models or maps. If you open a PDB model in Angstroms and a map with the scale set in nanometers then the map will look 10 times smaller than it should be relative to the model. Tom

From: Jeff To: "'Thomas Goddard'" <goddard@cgl.ucsf.edu> Date: Thu, 2 Nov 2006 13:26:11 -0800

thanks Tom,

sorry for a goofy question, but how do I know what units chimera is using (for measuring distances, having the output is nice in Angstroms, but sometimes (like with orienting a clipping plane) using unitless/pixels is more handy for displacements/etc)

thanks,

-jeff