What is inertia?

Inertia is the price of redirecting a pattern, and in OPH's account it equals the price of holding the pattern together, because both are the same work. Every object here is a pattern that repair, the step where neighboring observers settle a disagreement, must re-establish at every event. Changing the pattern's drift means renegotiating every seam on its boundary, every place it meets a neighbor, instead of reconfirming it, and holding it in place works those same seams at every event anyway. So a pattern twice as costly to hold is twice as hard to turn, and nothing else about it enters. OPH reads that standing cost as mass. Showing that it is the rest mass a balance measures is a step OPH has still to carry out on its executed observers. Two lumps of equal weight and different insides needing different pushes would refute the account. Left alone, a pattern keeps its drift, because nothing on its boundary needs renegotiating.