Hi Sarah, Chimera does not show sigma values for a crystal map in the volume dialog. It shows whatever values are actually in the map file. Here is a description of how to convert to sigma values: http://www.cgl.ucsf.edu/pipermail/chimera-users/2008-May/002651.html Chimera map display was primarily intended for electron microscopy, hence the deficiencies with crystal maps you are encountering. Allowing direct display of sigma values is item 153 on our requested features list: http://www.cgl.ucsf.edu/chimera/plans.html Tom Sarah Boyce wrote:

Thanks Tom. I also was wondering about the display options for the density. How does the histogram display level correlate to the sigma level of the map?

Sarah