Giles, That description is going to take at least two Martinis - stirred, not shaken, before I can comprehend your analysis. I was just going to set the boat up on a flat surface - parking lot. Get my current "actual" water line horizontal, by moving the trailer tongue jack up or down, and then with the laser on a ladder about 20 feet away, and the laser on a lazy Susan, rotate the lazy Susan and the laser to mark the water line. Maybe I think it is easier than it really is, but I will solve the problem when spring arrives. Meanwhile thanks for convincing me that I need a second Martini. Connie