I am drawing the line. As you can see, Furball is helping. When Pat came home for lunch he brought me a second roll of blue tape. That really helps. After the lines are drawn, I can lay both lines at the same time.
In case I do this again, I'll document what I've learned. First-- knee pads are a must! That floor is HARD. I tried various methods of drawing the lines. The easiest one doesn't even require a pencil. Just a good yard stick and the tape.
I place the yard stick near the wall and use the tape to mark the 12" point. I'll next use the second roll of tape to mark the 13" point. I press the first six inches down securely on each piece of tape so they won't come loose when I tug on them later. Then I move the yard stick about 1/3 of the way down the floor and position the edge of the stick on the starting point of this "brick". Using the first roll of tape like a plumb line, I "snap" it straight to the 12" mark and secure it to the yard stick. I now have a straight line. I repeat for the second role of tape, securing at the 13" mark. Press the tape down and progress to the next section of floor.
Quick. Straight. And no pencil marks to paint over if there is a mistake.