Given that the symbol " is the symbol for inches, and ' is the symbol for feet, I would suspect that there has been a mistyping in the quote.

I think that what was meant to be there was 72" or 72.1" (inches), which is exactly/one-tenth of an inch over two yards (one yard = three feet). That would produce the desired result of a nearly one-foot increase in the radius of the belt; adding 72 inches to the circumference of the belt would produce an increase of 11.46 inches (72 inches / (2 * pi)) in the radius of the belt, which in this case is the height above the ground.