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Romer Scale Grid: help with UTM

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I got the Romer Scale Grid from shavenraspberry. I have 2 1:50000 maps of the Pyrenees, they have the UTM numbers on each side. I'd like to find out with this scale the UTM position of a given peak. I can't seem to be able, I miss a video about this at the Learning Centre  :'(


Actually, I think I got it. But I have problems with one map.
Both are 1:50000 French map is ok with the Romer Scale Grid,  I have been able to more or less accurately plot some UTM locations. However with the map from Alpina Pub. (Spanish), each grid on the map is way bigger than the other one, so can the Romer Scale grid be used for the latter? See pic attached.

Thanks for your help in advance :)

captain paranoia:
I wonder if the grid on the Spanish map is an angular grid, rather than linear.  Have a close look at the scales on the borders.

Actually, the biggest clue will be the shape of the grids; if they're square, then it's likely to be a linear scale.  If they're rectangles, taller than they are wide, then it's likely to be angular; longitude circles are always the same size, but latitude circles get smaller as you move away from the equator, so a given EW angular change is a smaller linear change.

captain paranoia:
Having taken a look at the Editorial Alpina website, I see that their E-50 series maps appear to have a grid at 5km spacing (read the 'more info' notes).

So it may be that your map alse has a grid that's bigger than the 1km expected by the romer scale; Alpina seem to do this.

Looking more closely at your pictures, it does seem that the French map has a grid of 40mm.  So, it's either a 1:50k map with a 2km grid, or a 1:25k map with a 1km grid.

The Spanish map appears to have a grid 2.5 times the size of the French, so it looks like a 1:50k map with a 5km grid.

captain paranoia:
I've hacked a bit of PostScript to draw a 5km, 1:50k grid reference tool for use with these maps, a bit like a larger version of Lyle's tool at ShavenRaspberry.

Naturally, it's quite big (125mm by 135mm), but it ought to work.  It has a 10cm ruler, too.

I've uploaded the PDF to this thread, so you can download it directly.


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