Many symmetry-defined angles, such as the tetrahedral angle 109.471221...are
difficult to type. If SNAP is used, then any angle near to a
symmetry-defined angle will be adjusted to that angle. Thus 109.471 would become
arcos(-1/3) accurate to 15 or 16 figures. The tolerance of SNAP is quite strict,
so 109.47 would NOT be recognized.