Hello, I am trying to place a centroid https://www.cgl.ucsf.edu/chimerax/docs/user/commands/define.html#centroid marker at the center of a selection of atoms, for example in the middle of a benzene ring that is at some arbitrary position in my system. I want to do some distance measurements here. I can do something like this: shape sphere color orange radius 0.25 center sel where the center sel places the sphere where I want, but these spheres can't be used to make measurements. Instead I think I need a marker object, such as: define centroid radius 0.25 color orange But I don't know how to recreate that `center sel` position. I have tried define centroid radius 0.25 color orange position center define centroid radius 0.25 color orange position center sel define centroid radius 0.25 color orange position sel These do not work. I am under the impression that the centroid is a marker object and should have some position argument. Can anyone help me? Thanks, -- German Barcenas Ph.D Candidate | Materials Science and Engineering Materials Modeling and Theory Group Boise State University germanbarcenas@u.boisestate.edu | 940-577-5094