Hi, I am trying to understand how the plane is defined in chimera. Can you please help me with that? "Define a plane for the specified <https://www.cgl.ucsf.edu/chimera/docs/UsersGuide/midas/frameatom_spec.html> atoms. Eigenvectors/values are calculated from the atomic coordinates after subtracting the position of their non-mass-weighted centroid. The plane is anchored at the centroid and aligned with the first two eigenvectors (the third eigenvector is normal to the plane)." Define a plane for the specified <https://www.cgl.ucsf.edu/chimera/docs/UsersGuide/midas/frameatom_spec.html> atoms. - specified atoms, i use 'sel protein' Eigenvectors/values are calculated from the atomic coordinates - atomic coordinates, so x,y,z coordinates of all atoms. (Can you please explain a bit more like how and what you read from PDB file to define plane). after subtracting the position of their non-mass-weighted centroid - how is non-mass-weighted centroid is calculated The plane is anchored at the centroid - which centroid is this? Is the protein moved to the origin(0,0,0) position? Thanks, Catherine