With stirred glass delivery systems, cyclic variations in gob weights and gob throws (the angle at which free falling gobs land in the moulds), are caused by unsteady stirrers which are displaced from the delivery system's centre line and are rotating at speeds differing fom the gob rate. This loss of statistical process control disappears if the stirrer's rotational speed is synchronized. In this paper three equations are derived. One predicts the projected horizonal angle for the orientation of a gob as it lands in a mould. Another predicts the number of gobs before equal or almost equal weights repeat, and a third equation relates weight variation to wobble and to the radial location of the rotating stirrer or needle. This equation shows the symmetry that may be expected in weight variation curves.
