UKC

Hi, Does anyone know the history of the blue cooper OS bolt on the summit of Great How in Eskdale?

On the map I have it's marked as a trig point 🔼 but there's no pillar just this strange blue orb!

There was a time (1980s?) where the OS started demolishing trig-points. They stopped following a campaign, but that's all i can remember ...

Looks like the centremark under where the trig point stood that represents the actual datum point  The pillars are typically hollow down the  middle under the theodolite mount so a plumbline can be dropped down to centre it precisely.

It's a lightning conductor...

Just for clarity; that was intended to be a joke...

Shocking

The pillars have a tri lobed forced centring bracket on them to enable consistent accurate set ups of the instrument and targets. The instrument is mounted on a pillar plate which has pins that sit in the grooves. It also negates any error in the optical plummet of the tribrach. No plumb bobs are used.

But yes, the pillars have buried reference points underneath.

Not in normal use, no - it was the bracket itself that had to be centred during construction.

"Before the concrete sets, the brass spider, complete with holding down bolts, is set over the centre pipe and is carefully plumbed over the pillar bolt from a special temporary fitting to the spider, by sighting in both directions through the lower sighting tubes."

( "History of the Retriangulation of Great Britain")

Shocking news,bolts on mountain rock in the lakes. Chop it at once, it's the thin end of the wedge, this bolting needs to be stamped out at once. 

It’s actually a lightning bolt. 

But I just stand by and I wait my time

They say you gotta toe the line

They want the water, not the wine

But when I see the signs, I'll jump on that lightning bolt