J. Whittaker: Unpublished class paper, Anthropology Dept, Grinnell College. Moment of inertia is the tendency of an object to maintain its path of rotation and increases with the mass of the object and the distance from the axis of rotation. Thus a weight on a swinging atlatl stabilizes its motion and should increase accuracy. The greater the weight and the further from the handle, the more the effect, but the force necessary to swing the atlatl also increases.
Using 5 prehistoric atlatls found with weights attached, moments of inertia can be calculated, finding a narrow range. This "optimal" range of moment of inertia can then be used to model the most likely position of weights of other forms and sizes on atlatls.