Hi William, The volume data values Chimera shows in the volume dialog histogram are just the values found in the map file. They are not in sigma units. You can measure the root-mean-square value for a unit cell map with menu entry Tools / Volume Data / Measure Mean, SD, RMS and divide the reported values by the RMS to get sigma units. This is a pain. The reason it doesn't work better is because Chimera map display was primarily developed for electron microscopy where sigma values are not easily defined as in crystallography. Tom
Hello, I am trying to make an electron density figure using chimera and need to contour the F0-Fc map to 3 sigma. How can you determine the sigma level displayed with the volume viewer? The levels appear to be different than that observed when using coot or Xtalview. Thank you, William Snee