On the 9th Day of Trigmas the Ordnance Survey sent to me......Trigopoly - #9 Dallas
Another bolt for you here, top left of inspection hatch, you may need a spade to uncover.
Near to the bolt is a yellow sign with black writing on it, using this as your clue: Final =
N 57° 33.(4th Letter Plus 6th Letter) (5th Letter Divided by 4) (5th Letter Divided by 4)
W 003° 27.(5th Letter Minus 6th Letter)0(Last Letter)
Trigpoints are the common name for "triangulation pillars". These are concrete pillars, about 4' tall, which were used by the Ordnance Survey in order to determine the exact shape of the country. They are generally located on the highest bit of ground in the area, so that there is a direct line of sight from one to the next. By sitting a theodolite (an accurate protractor built into a telescope) on the top of the pillar, accurate angles between pairs of nearby trigpoints could be measured. This process is called "triangulation". A major project to map out the shape of Great Britain began in 1936. The network of triangulation pillars, with accurately known positions, led to the excellent OS maps which we enjoy today.
