spacemule said:Charging by the inch really doesn't make economic sense. Think about it--surface area of stumps is not directly proportional to diameter; rather, it's exponentially proportional. In other words, a 5" stump has 19.6 square inches of surface area. If we double the diameter to 10" though, the stump has 78.5 square inches. So, you're only charging twice as much for the 10" stump, yet you're grinding 4 times as much stump.