Dave,
Thanks for your reply. I am reminded that here I may have topographic maps from
late 1800's possibly and from the late 1950's. I will dig them out to see what
they show.
I assume the numbers you show are for London. Also I'd expect to find accurate
current values for my location on line somewhere.
It's just of interest - I don't expect to do any important surveying with this
Brunton Pocket Transit. I do want to survey our house lot. I think only one
corner pin is known.
I used to work at NIST/NBS Gaithersburg, MD. On the grounds there is a primary
survey monument. It is at the top of a 20-foot(?) pole anchored in bedrock and
covered by an innocuous cover in the grass. It and perhaps 2 or 3 others in
this part of the country establish the basis for all surveying this side of the
Mississippi. It's position is known to a small fraction of an inch. Also on
the site is a GPS monitoring system that issues corrections to GPS users doing
surveying. In that same building is the US standard 1.1 million pound weight.
Ferdinand Hassler was Superintendent of the first thorough survey of the East
coast sometime around 1800. See NIST.gov for info about him.
Roy Morgan
K1LKY Western Mass
> On Feb 21, 2020, at 9:39 AM, David Olean <k1whs@metrocast.net> wrote:
>
> Years ago, I think the correction was more like 17 degrees in New England.
> ...magnetic variations for London, England over the last few centuries. The
> pole really does move.
>
> YEAR DECL.
>
> 1600 8E
> 1650 1E
> 1700 7W
> 1750 18W
> 1800 24W
> 1850 22W
> 1900 16W
> 1950 8W
> 1970 7W
>
> 73
> Dave K1WHS
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