[Chimera-users] RMSD fit of an object to atom

Dear folks; Is there any simple way in chimera to do rmsd fitting of the object to the atom. I would like to measure the rmsd of an density peak with the atom. Could someone give the detail, how can I do it. And one another thing, how can I get rid of the problem with " At least four atoms should be selected", I am interested to do 'match' for two atoms. Thanks a lot, Navnit