When four atoms are selected, this will calculate the torsion angle that the four atoms form and display the value in the message window at the bottom of the screen. The torsion angle depends upon the order of selection, with the second and third selected atoms forming the intersecting line of the two planes, and the first and fourth atoms defining the two planes. The first plane contains the first, second and third atoms, and the second plane contains the second, third and fourth atoms.
