[Formerly Steve Wilkinson]

I have no idea what it costs, having only done it myself, but I find the easiest way to explain corner balancing is to imagine you're sitting on a big, four-legged chair. First time you climb into it, only two of the legs are actually touching the floor, so the thing sort of rocks back and forth because there's a quarter-inch gap between floor and leg on two of the legs. You need to adjust the length of all four of the chair-legs so they're touching the floor equally, and are doing so with you sitting over to the left side of the chair, which is where you like to watch TV, like you would be if you were in the driver's seat of a car.

Where this becomes tricky is that imagine the tippy-two-legs chair, and it becomes obvious that you could simply screw away on the adjustment of one of the two short legs and get the chair stable, all four legs touching the floor. But the chair probably wouldn't be level. What you need to accomplish is to adjust the chair legs so that ultimately the chair is perfectly level (with you sitting where you normally do to watch TV) and that each of the four legs is exerting the identical pressure on the floor.

Trickier yet: Maybe you don't want identical pressure on all four legs but some differential front-to-rear or even side-to-side that you have predetermined will make your, uh, chair handle better.

That's corner-balancing. Not easy.