The owner of the reservoir doesn’t bother to measure it in square miles, he measures the acreage. Then the acre–feet becomes a trivial computation. Yes, if pres

The owner of the reservoir doesn’t bother to measure it in square miles, he measures the acreage. Then the acre–feet becomes a trivial computation. Yes, if pressed he might dredge up the obscure fact that a square mile is 640 acres, but then he would have to do long division to convert it, and the whole point is to avoid that kind of complexity.