Random. This is 75% of my job normally. For every beam, column, brace, ladder, stair, handrail etc.. on a structure. Design drawing is normally just a line for a beam and the size. I fill in the rest so it can be fabricated. Most of the dimensions for holes are from the end of the beam so it can be put into a CNC beamline machine or laid out with a tape measure. NS and FS, Near side and Far side.