As far as I know that would require the $50,000 GPS setup. I work for a survey & engineering firm and that's how much the equipment costs that locks into the satellites and can give accurate vertical and horizontal elevations to the hundredth of a foot. The small hand held units generally are only accurate to within 10 feet vertically and horizontally. So they wouldn't be good for setting a main line. There is a "smart level" on the market for around $100 that can be placed on the main and will tell you the % slope, very handy.