|Application of the old adage "Water seeks its own level"!|
I could rent a rotary laser level for a day, but that's a lot of money and hassle. So we put the laws of physics to use and employed a twenty foot length of tubing. I siphoned water into it, leaving about a foot and half empty at each end. Then we just held one end of the tubing next to the desired starting point and walked the other end around to different points in the room, waited for the water line to level out each time before making pencil marks on the wall. No need to pull it taut; the tubing can lay on the floor, coil up, run over obstacles, etc. (just no kinks). You can buy or make devices with a water reservoir that are more accurate, but this served our purposes. It does take two people, but that just gave Jeff and me some more togetherness!