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Finding 6 digit grid ref Letterboxes - How to calculate

Posted: Fri Jan 13, 2012 5:50 am
by blue danube family
Just wanted to ask how to go about finding 6 digit grid ref Letterboxes and how to calculate.

I learned once that in Memory Map I can draw lines from given points that are mentioned in the clue and see how all three lines cross at a specific point where the box is. Also read that I have to add or subtract ┬░degrees.

But somehow using the many 6 digit grid refs I have I never end up with all three lines nearly near each other ... Anyone know how to calculate using Memory Map. Also after plotting on the map, also how to use the Silva 54 compass or any compass then once I am in the area of the box. I seem to always walk in one direction noticing that I am near the second point to target, but then the third point to target does not match at all.

Also does anyone of you have the old Word docs, where many many given obstacles, known places, poles etc. are listed, there are Word documents around that are older than 2000 and have this information I believe from the 90ties.

Posted: Fri Jan 13, 2012 8:49 am
by Sowerby Streaker
Hi, you are experiencing difficulty reading compass and map because you have come to rely soley on your GPS. I use GPS but also still take compass and use that for the clues. If I get 'stuck' then out comes the GPS. If out on the moors you get one bearing correct and the other is out, you have to keep walking in line with the correct bearing until the other one comes into line. The 4 fig grid given with the clues will put you in the correct square, then you work it out from there. Think the tolerance is 4deg from map to moor, but am sure others will put you right on that one. In the 'good old days' we only ever used compasses, before the GPS was made commercially available in hand held form (and affordable), so are used to using the compass.

Posted: Fri Jan 13, 2012 8:55 am
by blue danube family

Still, how do I do the Memory Map meassuring/calculations with drawing lines and finding the right spot.

You are right, I relied many years on the GPS.


Posted: Wed Aug 13, 2014 10:47 am
by blue danube family
any thoughts on this issue how to do it with memory map software?

Posted: Thu Aug 14, 2014 10:01 am
by Box Hunter

I don't know how the memory map software works, but I doubt it will solve your problem, because the bearings given in the clues are only as good as the skill of the person who placed the box in the first place. Most are pretty good, but not always. If they don't have a steady hand, if they don't hold the compass level, if it has a bubble in it or if they don't look through it straight, or even if it is windy, then the clue may be inaccurate. In addition, even if you have a ten-figure grid reference for a given tor (for example), they are quite big features, and if there is a sub-description ("leaning stack", "most southerly outcrop", "logan stone on...", etc), there is likely to be an error there. Finally, if it is an old clue then the magnetic variation will make life more difficult as time passes. That is why the local clue (describing a recognisable feature in the immediate vicinity of the box) is so important.

I'm afraid there is no easy solution to this, and a lot of these clues just need time and patience to solve once you are on the ground. I use the "Point Intersect" function in Colin Masters' letterboxing programme, which has the precise locations of thousands of points programmed in, but it can still be a considerable distance out, and is rarely spot on (and can only take two bearings at a time); I use it as a guide to get to the right area only.