11 points.

Of course, not the only visible mapping feature celebrated today.

Triangulation points.

Of course.

We will come across it by accident or design seven more significant historical interest in others.

Exactly.

Our trip points normally for free concrete blocks located at high point within a certain area used by the Ordnance Survey to map the entire country.

The idea being you have at least two others in plain sight.

You place a device in here, measure the angles between two and you could triangulate whole country.

Well, not the whole country.

With these two big, you get the idea.

This was accurate across the whole of the country to within 20 meters.

Thinks, however, do you three millimeters in the form that we know them today.

Triangulation points were built from 1935 omelets and they were built to aid the real triangulation of Great Britain, which, of course, employees there was triangulation before this on.

Of course, they're waas.

Principal triangulation of Great Britain took place between 17.

91 at 18.

53.

Which brings us nicely to this trick point here.

So have a look at Beacon Hill on any old map which predates the re triangulation of Great Britain on Lost this concrete structure and you see the map states gun end of base in this point here contained just that the upturn muzzle of a cannon stuck out the ground on in math.

In terms in this country that was extremely significant.

Why?

Because if you walk south of this point right about seven miles and stand in a pick field just north of Salisbury, you just walked along.

What was one of two original bass lines for the original principal triangulation?

Thea.

The one could be found in hams like it's unknown whether the cannon's still survives here today, but I'd like to believe it does.

Why not turn muzzle cannon?

Well, possibly because Artilleryman Williams much it was one of free.

They were tasked to undertake the mapping.