jono300

iTrader: (8)

Whilst out walking the dog up the local hill come across a concrete tower with the words " triangular oridance survey station " written on the top surface off it, just a small 3-4 foot structure with a few markings on the top, although not clear it does not appaer to be actual compass points.

what exactly is it, and how do you use it ??

CrisPDuk

The peaks of prominent hills are marked on OS maps, the pillar is like a big you are here sign which correlates exactly to the map reference.

BOB.T

Was it square, white and the thing on top, did it have 3 pointy things on it?

It sounds like a Trig point to me. OS use them and two others to form a triangle and then use the angles and maths to figure the distance between the 3 points. It's how the first really accurate maps were made.

Have a look here, http://www.jeremyp.net/trigpoint/index.php

Chelspeed

It's called a Trig Point. Abrreviation for triangulation point or trigonometry point. They're shown on OS maps as small blue triangles on the top of every five or six adjacent hills.

Used to be used by Ordnance Survey to make maps, they clamped a theodolite to the top, that's what the big brass grooves are for on the top. They'd then take a bearing to two other trig points on other hills and use the angles between them to generate the maps using o level trigonometry (which I understood 30 years ago...). Sure they now use GPS or satellites or whatever instead but the trig points are still there.