Hi Elaine, I try to set values below certain level to 0 in a EM density map (mrc format) using vop threshold: vop threshold #0 min 0.00007 set 0 But I got an error message: Unknown vop operation: threshold The Chimera version: candidate version 1.7 (build 38162) 2013-01-25 00:38:47 UTC Could you please help me out? Thank you very much! Zongli