The comparison to a flagpole-sitter is perhaps misleading, for the post does not end where the mill house begins. Rather, it enters the body of the mill through a loose fitting collar beneath the lower floor and extends about half-way up into the mill, where it ends in a pivot bearing. The entire weight of the mill—sails, body, millstones, shafts, gears, grain, meal, and miller (to say nothing of the mill cat, kittens, and resident mice)—rests on this single bearing at the top of the great post. Keeping so much weight in stable balance was no great problem for the millwright as long as the mill did not move. The collar or ring bearing around the post kept the body from tipping far in any direction—or was supposed to. Moreover, the millwright estimated the weights of the various elements and positioned them appropriately about the pivot. Of course, things sometimes came out wrong. A mill that tipped incurably forward was called “head sick”; one that always tipped backward was “tail sick.” When the mill was in motion the matter of stability became a good deal more complicated. For various reasons, including aerodynamic and gyroscopic effects that the early millwrights sensed but did not fully understand, the balance of a windmill is different in operation than at rest. The successful millwright, therefore, needed an accumulation of trial-and-error knowledge that might go back for generations. The result, even though most everything but the millstones was of wood, was a surprisingly stable and exceedingly durable structure. A post mill built in Lincolnshire, England, in 1509 was still in operation in 1909! And although any storm might leave tragedy in its wake, post mills toppled over less often than their precarious position and top-heavy appearance would seem to promise. In this respect the Williamsburg mill is doubly guarded, being equipped with removable metal braces and buried ground anchors for use in the event a hurricane is predicted. This adaptation, to be sure, is a twentieth-century safety measure, not an eighteenth-century custom. The problem of balance, and the related difficulty of maneuvering a post mill to face the wind because its whole weight is focused on the one bearing, generally limited such mills to one or two pairs of stones. Some English post mills had three pairs and a few even four. But these exceptions demonstrate the limitations of the post mill and the reasons for development of its successor, the tower mill.