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. Line Jerry-B7 is longer and oriented more east-west than Jerry-A1 so the magnitude of its arc-to-chord correction should to be larger.

We've shown that both arc-to-chord equations give the same results so we'll use Equation H-10.

The correction for Jerry-B7 is larger than Jerry-A1's as expected.

At Jerry the correction to A1 is negative (angle left) and to B7 positive (angle right). The angle and corrections are shown in Figure K-7.

Figure K-7
Angle Corrections

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

The user must decide if combined bascksight and foresight arc-to-chord correction is significant.