Gridded Charts Q
I posted up the following Q recently and gratefully got a reply from, I think 'Send Clowns', here is that Q:
Q: A Northern L.C.C is overprinted with false grid. Constant of cone of chart is A. At B degrees West the grid track is C and the true track D. At which longitude is the false grid aligned?
The below is CS's reply which I found very helpful. However being dim I don't understand the part that says 'also whether E or W'. I would appreciate further information/explanation with respect to that part of the explanation and suggestions for a diagram to aid visualisation. Thanks in advance.
Ans: Comparing C and D will give you the chart convergence, and also whether E or W. On a Lamberts chart, convergence = change of longitude (from the datum) x sin of parallel of origin (or 'n' factor). Therefore, change of longitude = chart convergence/'n' That change of longitude is the difference between B and the datum.
You now have to work out which sense to apply it . In the N hemisphere, if convergence is W, B is E of the datum. In the S hemisphere, if convergence is W, B is W of the datum.