Dear All, I have a map (A.mrc). When I open it in chimera (the map should be #0), the Volume Viewer shows the Range is -0.618 to 1.63, the default Level is 0.175. With command "vop threshold #0 minimum 0.18 set 0" I got another map (let us call it B.mrc, should be #1), the Volume Viewer shows the Range is 0 to 1.63 (understandable, the maximum value is still 1.63 as in A.mrc, the minimum value is 0 as for all values not higher than 0.18 has been set to 0), the default Level is still 0.175. Immediately I run the command "vop threshold #1 maximum 0.17 set 1". Before I running the command, I guess all the density value should be either "0" or "1", because all the value lower than 0.18 has been set to "0", and all value higher than 0.17 has been set to "1". However after I run the command "vop threshold #1 maximum 0.17 set 1", I got another map (let us call it C.mrc, should be #2),the Volume Viewer shows the Range is 0 to 0.17 rather than 0 to 1, and wen I change the Level, the image of #2 changes correspondingly with the Level from 0 to 0.17. Here I would ask, why the command "vop threshold #1 maximum 0.17 set 1" did not lead to a map with all values greater than 0,17 as 1? How to get a map based on A.mrc so that all values less than 0.18 as 0 and all values greater than 0.17 as 1 (please tell me the specific method)? Is any significance for the obtained C.mrc with range from 0 to 0.17? I am looking forward to getting your reply. Smith