Trigs on old maps question

[alansmeaton]

Hi all,
It's getting muddy out there!

I was looking at some old OS map reprints of my local area, dated 1899 and on them are a number of small triangles representing 'trigonometrical stations'. A number of these seem to be situated in the middle of fields - what form would these take and how would their precise location be determined? Just wondering.
Thanks
A

[agentmancuso]

These are likely to be stations used in the Primary Triangulation which took place in the first half of the 1800s. At times the same location was reused in the 1936-62 Retriangulation and hence referred to as 'Old Trig' in the OSGB36 database. Very little evidence of the primary triangulation has ever been found on the surface, though I understand there may be buried stones in some cases at least.

[alansmeaton]

OK, all is clear. The only thing that puzzles me is why these spots were chosen, why not somewhere more elevated or easier to measure an exact location to. No doubt there were good reasons at the time.