Lanchester's rule

Lanchester's rule

[′lan‚ches·tərz ‚rülz]
(mechanics)
The rule that a torque applied to a rotating body along an axis perpendicular to the rotation axis will produce precession in a direction such that, if the body is viewed along a line of sight coincident with the torque axis, then a point on the body's circumference, which initially crosses the line of sight, will appear to describe an ellipse whose sense is that of the torque.