Everything about a cheval mirror lives or dies on the pivot, and the pivot is not at the middle of the plate.
An oval frame carries more mass low down than high, so a mirror hung on trunnions at its exact geometric centre will always want to fall forward. Our artisans find the balance point of the finished, glazed frame first - actually balancing it on a bar before the trunnions are bored - and then set the pivots a small distance above that point. The frame is left very slightly bottom-heavy, so it returns gently toward upright rather than tipping away from you if it is nudged.
Friction is the second half of it. Leather washers are fitted at each trunnion and tensioned so the plate moves under the steady pressure of one hand and then stays exactly where it is put. Too loose and it drifts while you are looking at it. Too tight and you need two hands and a firm shoulder.
The result is a mirror you set once and forget about, which is the entire point of the form.