4. Ground to Grid Angle

To convert angle B7-Jerry-A1 to grid, we need the arc-to-chord correction for lines Jerry-A1 and Jerry-B7. We have the former, now must compute the latter. Although line Jerry-B7 is longer it is oriented more east-west than Jerry-A1 so the magnitude of its arc-to-chord correction should be smaller..

Since we've already shown that Equations H-11 and H-12 give that same results, we'll use the latter to compute the correction.

As expected, because of the line orientation, its arc-to-chord correction is smaller.

Figure K-8 is a sketch of the angle with all parts in place.

Figure K-8
Angle Correction

The grid angle B7'-Jerry-A1',  βG , is:

The total effect of the backsight and foresight arc-to-chord corrections amounts to only 00.20" which may be small enough to disregard.