I'd like your opinions on this. When taking compass readings on a symbol to get it accurate wouldn't you have to consider the declination at the time say a carving was made? If I understand it right the magnetic pole it always changing . So what is 90 degrees now would not be the same say 100 yrs ago. Right? Hope I am explaining that clearly.
magnetic declination????
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Jason in Enid
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Unless you are taking an azimuth reading in northern Canada, don't worry about it. The tiny shift is less than your walking or sighting variation.
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Thank - you Jason but on the noaa declination chart for my area in 1810 it shows a difference of 8.5degrees east which means I would subtract that from my current reading. walking 100ft would make a substantial difference. I think maybe 15, 20 ft. Also you mention variation - does that mean what metal objects are around you at time you using compass and the pull they have on it?
Jason in Enid
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The deflection in the course of 100 feet is almost nothing. 8 degrees is like taking a big step to the side. AS I said before, the error of your human eye sighting or walking will be bigger.
Like Franklin said, if you are talking about a mile, that is something to consider but that is not compass work, that is map work. If you are doing map work, you have to know both the mag change as well as the grid-compass deviation. You should probably pick up a copy of the Army Land Navigation handbook. I could teach it all to you in a day, but I'm not free.
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by my calculations with my location 150feet would make 24ft difference in 1810. Today the declination difference is only 1.3 which would be nothing to really worry about. But since I dig with shovel and not a back hoe wow- don't think I'd hit it. Thank-you both for opinions. This seems to me a very important issue and wish it was discussed more here. Noaa has a great site for declination charts and if your east of the Miss. river it goes back as far as 1750s.
Jason in Enid
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How are you getting your calculations? Try this... take a compass, go outside and walk 150 feet from an object, now shoot an azimuth to that object. Now turn until your compass is reading 8 degrees difference. Do you see 24 feet between your two points?
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Ok Jason - good test but I want you to know I was out in the pouring rain doing it, ha. I didn't use a measuring tape but walked it off (which I am pretty accurate at that from past experience) I counted 6 to 7 paces at 3' a pace is 18 to 21'. I am assuming why we are using the 8 is due to my first post? How I came up with 24' is rough. Did it on google earth. I took compass reading I'm interested in and subtract the declination which I then put both on google earth and use there ruler to measure the distance. I will recheck this when it is not pouring.
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Ha , don't we all wish we were where we're suppose to be. Yes Franklin I get it and 100% agree. This is so, so very important stuff. Thank-you for your time and kindness. My next step now is digging Hoo-ray. I pm'd you too.
p.s. yes I understand what you mean about east and west. Take Care
p.s. yes I understand what you mean about east and west. Take Care
Of Course you all know that there is a government sight that you can go to to find out how much magnetic north has changed for your area, right! All you have to do is go to: http://www.ngdc.noaa.gov/geomagmodel.../historicPoint type in your zipcode and year,,,,,yada yada
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