Survex Digest, Vol 4, Issue 3

[Philip Balister]

Here on the east coast of the US declination is around 6 degrees and
moving about .1 degree per year.

I  look up the current declination here:

http://www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp

It is pretty important to keep track of the declination, especially as
projects strecth out over several years.

Philip
 
On Sat, 2004-10-09 at 04:28, Mike McCombe wrote:
> > Michael Lake said:
> >
> > | The mag declination correction for a given area might not have a linear
> > | relationship with the date. Sometimes it is given as so-many degrees per
> > | year on a map but sometimes it's given as a table of values. I'd rather
> > | have to add a correction explicitly myself than survex guess it for me
> > | and not realise it. Also if I get the data wrong for a map by entering
> > | it incorrectly then the mag dec would be wrong too.
> > |
> > | my 2c worth.
> > |
> > I agree. Not only that, but many people calibrate their compasses in such 
> > a
> > way as to include both compass error and magnetic deviation in one figure.
> > Letting Survex deal with one part of this (I do not see any way in which 
> > it
> > can automatically deal with my compass!), will either lead to confusion or
> > to some folks not doing it correctly - or at all!
> >
> > Graham
> 
> With daily variations in magnetic declination in the UK typically 0.2 - 0.5 
> degrees (see http://www.geomag.bgs.ac.uk/observatories.html for examples) it 
> seems to me to be good practice to calibrate the compass against a known 
> physical baseline at the start of each day's work. Just taking the published 
> long-term rate of change of declination would be a poor second-best and not 
> something to be encouraged!
> 
> Mike
> 
>