Hi, folks! I have a problem about the measurement of torsional angle. In the chimera users' guide about the command angle, as follows, it says that if I select the atoms simultaneously, the order information will get lost. How can I keep the order information since I need it to calculate the angle I want exactly? For example, in the following command I originally want to calculate the n-ca-c-n(182) dihedral, angle :181.a@n,ca,c:182.a@n but in fact what chimera gave me was may be c-ca-n-n(182). I want to calculate a lot of diheral information so I can not click one by one in the gui mode, I wonder is there any way that I can get what I want . Thanks! Usage: *angle* *atom1 atom2 atom3* [ *atom4* ] *Angle* reports the bond angle for three specified<http://www.cgl.ucsf.edu/chimera/1.2199/docs/UsersGuide/midas/atom_spec.html#basic>atoms or the dihedral angle for four specified<http://www.cgl.ucsf.edu/chimera/1.2199/docs/UsersGuide/midas/atom_spec.html#basic>atoms. The order of specification is important, but atoms need not be connected. The angle value in degrees is reported in the status line<http://www.cgl.ucsf.edu/chimera/1.2199/docs/UsersGuide/chimerawindow.html#statusline>and *Reply Log*<http://www.cgl.ucsf.edu/chimera/1.2199/docs/UsersGuide/reply.html>. The atoms can be specified collectively using the word *selected*, *sel*, or *picked* if the current selection<http://www.cgl.ucsf.edu/chimera/1.2199/docs/UsersGuide/selection.html>contains only the three or four atoms of interest; the order in which the atoms were selected<http://www.cgl.ucsf.edu/chimera/1.2199/docs/UsersGuide/selection.html>(most likely picked<http://www.cgl.ucsf.edu/chimera/1.2199/docs/UsersGuide/selection.html#pickse...>) is used. When order information is lacking (for example, the atoms were selected simultaneously), the angle actually measured may not be the one intended. There are no automatic updates if the angle changes. A new command must be issued to measure the changed angle. -- Chao Wu Currently: National Institute of Biological Sciences, Beijing Huang Niu's Lab http://www.nibs.ac.cn/ Tel: 80726688-8572 Address: Beijing ZhongGuanCun Life Science Park, NO.7 Science Park East Road, NIBS B427 Postcode: 102206 Life Science Honors Program, China Agricultural University PO.1055, NO.2 YuanMingYuan west road, Beingjing, 100094 P.R. China Tel: 86-10-62812484 E-mail: lynnwuchao@gmail.com