Hi Sabuj, Chimera currently has no capability to display standard deviation values for volume data. It would be useful if the volume viewer dialog had an option to use sigma units. Could you tell me what crystallographers define "1 sigma" to be for a density map? Is it the root mean square density value over the entire map? For now here is a Chimera tool to report mean, root mean square, and standard deviation values for a volume data set. http://www.cgl.ucsf.edu/home/goddard/temp/volumestats.tar This archive contains a directory VolumeStatistics that you put in your Chimera distribution in chimera/share or on the Mac in Chimera.app/Contents/Resources/share Then when you start Chimera you will have a new menu entry Tools -> Volume Data -> Volume Statistics that reports the values for the current volume viewer data set, printing them in the Chimera reply log (menu entry Favorites / Reply Log). Tom