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ThisOriginalSource t1_j7e4ri8 wrote

Reply to comment by Synensys in Lead Plates and Land Claims in North America and Europe: When did the practice begin of burying lead plates to establish ownership of land, and why did it die out, and was it ever used successfully in a court of law to establish ownership? by whyenn

Can you share more information about this, or a source?

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noahjsc t1_j7eb47h wrote

I can explain this a bit as I learned a bit of orienteering from youth groups/military experience. So when working with a compass you have to actually modify the declination a bit. All this is rotating the angle markers. To determine that requires a little bit of math. This is because True North location actually moves over the years. So what he's stating is that the bearing to the location has shifted. As if you had a compass set to 0 declination which means 0 points at true north the bearing would be different.

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Quick explanation on what a bearing is. So when using a map the lines straight north are considered 0 degrees. East is 90, South is 180 and West is 270. So by drawing a line from one point to another you can use a protractor or other angle measuring tool to determine the angle.

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If the map is new and set properly to true north there is no declination set on the compass. So what you do is you rotate the right so that the angle you determined from the map is set to the front of the compass. You then rotate the compass(typically by moving yourself as you point it outwards from your body) till the north on the magnet and north on the reading align. You then know you are pointing at your bearing.

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With declination you have to adjust that angle a bit(usually compasses have a key to do it so you don't have to adjust on calculation). So on an old map you calculate declination and then when you shoot your bearing you'll still be pointed to the right location. However if you didn't calculate for declination cause true north moved you'll be facing a few degrees off.

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I'm sorry if this explanation is confusing. It's typically best done with a physical compass and map to show what i'm talking about. I tried my best to do it in writing.

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tropic420 t1_j7eel75 wrote

A physical compass and 2 or more maps of the same area some years apart, it would seem

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Synensys t1_j7fy7ne wrote

The basic idea is that magnetic north moves around over time (magnetic north and the north pole are not the same location). So if your boundary line is defined as a north south line, and you look at a compass to figure out where to put your wall, over time the direction that wall points relative to older walls, will change.

So present day scientists can use the orientation of the walls to track changes in the location of magnetic north pole.

https://theconversation.com/old-stone-walls-record-the-changing-location-of-magnetic-north-112827

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