I built a grade checker, using scrap lumber, a 12" level and drywall screws.
3 - 12 1/4 inch long 1"x 2"s
Lay one flat and the other 2 on their sides on each side of the flat piece.
At exactly 12"" from one end, drill a pilot hole and insert a 1" drywall screw up from the flat bottom( the top shouldbe the channel side). Make sure the screw is centered between the sides. The pilot hole should be tapered enough so the flat head screws in and is flat with the bottom of the wood.
Place the checker on a level surface and place the level between the sides of the checker (so it will not fall off, sides were added later in its development because of falling).
Of you you know the grade you want or need, calculate the rise per foot and back the screw out that amount.
Setting you checker on the subroadbed. The level should remain level throughout the grade.
I have double stacked helixes on my railroad and the checker was very valuable in keeping things consistent.
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