I nailed two 2x4s on the plank near one end (F22) perpendicular to the centreline and level. I then nailed two more 2x4s on the plank exactly 101.75" from the first set. The measurement is taken from the outboard side of both sets. The 2nd set was also perpendicular to the centreline and level. 101.75" was confirmed across multiple locations along the 2x4s.
