Crows foot

#1
No its not a bad case of athletes foot - but:

I was out on a walk with 0B at the weekend and on getting to a Trig point she pointed at the crows foot stamped on it and asked 'wossthat then'.

I informed her that it denoted that it was or had been owned by the military, to which she replied - why did they use a crow's foot as a symbol.

I muttered something about young ones joining being called crows etc. But can anyone provide information about why the crows foot seems to be stamped on everything military - and why a crows foot.

I await masses of well informed discussion on this point.
 
#3
It is the Broad Arrow of Sydney.

There's a thread in here somewhere with a full explanation - or do your own googling, you idle twat!
 
#5
The Broad Arrow has been used as mark on government property for a long time, civil and military. There's some information here although it doesn't really explain why it was first chosen.

Broad arrow - Wikipedia, the free encyclopedia

The Ordnance Survey was established for military mapping purposes. I was told recently that the reason deciduous and conifer trees were mapped differently was because the deciduous ones won't provide cover from view in winter. I'd never heard this before but it sounds plausible. The three armed metal shape on a trig point is there as a mounting for a surveying theodolite.
 
#6
It's not a crow's foot. If you look a bit closer, you will see that it has a horizontal line above the arrow. This is a Bench Mark and is a mark to indicate a height above sea level for surveying etc.

The only thing to be aware of when using them, is that the level information can be in either Imperial or Metric units.
 
#7
Retriangulation of Great Britain - Wikipedia, the free encyclopedia


How is a Trig Pillar Made?

The "History of the Retriangulation of Great Britain" by the OS. tells us that:

"The lower buried centre mark, consisting of a brass bolt set in concrete, is first inserted at a sufficient depth below ground level to be independent of the pillar of the pillar foundations. This depth naturally varies with the soil; on boggy ground, which is sometime encountered on hilltops, it was sometimes necessary to excavate as much as 15 feet before reaching rock or firm soil on which to emplace the lower mark. In such a case a correspondingly deep pillar foundation is necessary, whereas on out-cropping solid rock, a bolt is simply cemented in a hole drilled in the rock.

The lower centre mark and its concrete setting is covered with a small wooden box (which eventually disintegrates) to prevent adherence to the pillar base, and so to prevent disturbance of the lower mark in case the pillar should be moved.

Concreting of the pillar base was commenced immediately over and around the box covering the lower mark, without interposing any loose earth or stones, which might weaken the pillar foundations. Concreting the pillar base is continued up to ground level where it is left rough to set. Four angle iron bars are set in the base to project well up into the corners of the pillar, as a means of preventing fracture between the base and the pillar. The pillar bolt (upper centre mark) is also set in the base; it is arranged vertically over the lower mark by means of a plummet and marked board resting between marked pegs, previously fixed in correct relation to the lower mark.

The pillar bolt is next covered with a small wooden box, which is provided with side holes (to take the inner ends of the four sighting and drainage pipes) and a top hole (to take the lower end of the galvanized pipe running down the centre of the pillar).

Wooden shuttering, which may be taken apart and used again, is next erected on the pillar base. This shuttering has four side holes to take the outer ends of the four sighting pipes, which are then inserted, and a wedge fillet to which the level flush bracket in one side of the pillar may be wired in a vertical position. It also carries wooden corner fillets to provide an automatic chamfering to the edges of the pillar.

The centre pipe, which serves as further reinforcement, is set in position and plumbed, the plumbing being continually being checked during concreting. A good 4:2:1 mix of concrete, containing sharp well-washed sand and crushed stone as aggregate, is then poured into the shutteringand rammed. 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.

Concreting is then carried up to the top of the spider with an allowance of about 3/8 of and inch (a depth to which some pillars are suffering depletion from frost damage today) for later settlement of the concrete.

After a day to set, during and after which the green concrete may need protection from frost by a liberal covering of sacks, the shuttering is removed and the pillar is faced with cement plaster, to prevent possible disintegration by ice forming in cavities. Three of the sighting tube openings are plugged with paper and lightly cemented over to conceal their presence from visitors, who are often apparently unable to resist the temptation to stuff any 'foreign body' that comes to hand into the tubes. The fourth tube must be exposed to allow condensation to drain out of the pillar."
 
#8
You will find BM's all over the place - best spots being on churches and railway bridges. The larger the BM, the older it is and it is not uncommon to find a newer, smaller one on the same building - but at a different level. Also, if you have one on the side of your house, you cannot refuse requests to use it - it is the property of the OS and not yours!
 
S

syledis

Guest
#10
So that's solved, but where did the Camel Toe come from?
And more importantly, who put the ram in the ram alang a ding dong

Ok marks out of 10 for an RA bods here, whats the lat and lon for the trig pillar on the gun line at Larkhill?
 
#11
And more importantly, who put the ram in the ram alang a ding dong

Ok marks out of 10 for an RA bods here, whats the lat and lon for the trig pillar on the gun line at Larkhill?
That the one OS says doesn't exist.... Yet does?




Sent via Heliograph from the Jebel Birkenhead
 
#12
cheers chaps - especially queensman - 0B agreed with your supposition - that of being an idle twat. I shall now go back to examinng my collection of belly button fluff
 
#15
That the one OS says doesn't exist.... Yet does?




Sent via Heliograph from the Jebel Birkenhead
If OS says it doesn't exist, then more than likely it is a BP.
 
#17
cheers chaps - especially queensman - 0B agreed with your supposition - that of being an idle twat. I shall now go back to examinng my collection of belly button fluff

So you believe that it is not a Bench Mark as I said?....Queensman has to be right and all that levelling I did as a land surveyor, all wrong!

To clear this up, did it look like this?

saint-marys-church-os-benchmark_240.jpg
 
M

Mark The Convict

Guest
#18
Still to be seen carved into the convict-hewn porphyry kerb stones around inner Brisbane.
 
#20
Isn't a trig pillar by definition shown on OS maps? The same would apply to benchmarks surely, not much use as a datum without the data.
Usually are yes. As I said earlier, be careful when using a BM when there is more than one on a building - normal Ranger type maps don't show BM's - at least not al of them (been a long time). If the BM is shown and the figures are in italic, then it is in feet - no matter what the size, normal script means it's in metres.

IIRC, Bench Mark data is sold on AO sheet printouts for the region required and the scale shows individual property layouts and the exact location of the BM.
 
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