Lee Smith follows up Section - 12B: Measuring field pipe with this article about finding odd angles in the field.
The 3/4 Method
Sometimes, mostly never, things do not get installed in the field as square as they are on our models and drawings. So we either need to locate these things for future additions.
We can use the "3/4 method" for determining the angle. You will need either (2) spools of twine or (2) long tapes (100ft) and a small tape or carpenters rule. For this illustration, we will use twine. Note, the twine may not be needed if the item you are wanting to find intersects with a point you can easily locate.
Along with the item you want to locate the angle of (Object 1), you will need have an object or item to associate with (Object 2) that is known from others point on site.
Stretch one twine along Object 1 till it pass Object 2. Stretch a second twine along the known Object 2 till it passes the first twine. Locate the point where the two twines intersect and mark or clip them together.
From the intersection, measure along one twine 36" (side "A") in either direction and mark the point. On the other twine, measure 48" (side "B") on either side and mark the point. Now, you have two known points from the intersection. Measure across from one mark to the other and find the distance between the two known marks, this will give the length between the known points from the intersection (side "C").
Know, using the formulas from an oblique triangle, you can solve for the angles of the triangle using sides A, B, and C.
About the Author
Lee Smith is the Owner/Operator of Smith Design, CADWorx and AutoCAD experienced,