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I propose the following procedure for Index correction
for back sights on land. It seems simpler, and independent
of the index correction for the fore sights.

Choose two distant objects in opposite directions.
They don's have to be too distant. Horizontal edges
of roofs of the buildings
will be OK. Or two assistants holding some poles.

The difference in bearings should be 180d.
Now measure the vertical angle between the directions
on these two objects by a back sight.
Then do the same with your quadrant upside down.
One angle will be negative, another positive.
Their algebraic sum, divided by 2 is your index correction
for back sights.

Remark. Taking a back sight with your quadrant upside down
may be somewhat tricky: you have to incline your head
to horizontal position. Not to obscure your back sight
with your body. You may need another assistant for this
(to hold your body from falling:-)

Alex.



On Sat, 20 Nov 2004, George Huxtable wrote:

> I am especially interested in this matter because Lewis & Clark

> On land, the following procedure seems plausible-

   

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