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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.
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| 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.