I didn't do a VDI number since I was using the E Trac. I was mostly just doing what you did. Look at the box, look at where it enters the house, and detect the line straight between them. If you get a signal almost everytime you go over that line where you think it is...you are there lol That's the only way I know how to trace a line. When I dig for one, I dig a shallow plug sideways and not down, to minimize the cutting the line factor. Deep plugs will cut the line, but just skimming the grass may save you a lot of headaches.