Thursday, March 20, 2008

How to be an Archaeologist: Spot Levels and Benchmarks (Part Three)

Okay…hands up any of our readers who managed to solve the problem of how to take the ‘spot level’ reading at point ‘A’ from point ‘D’ as encountered at the end of the second part of this article? (Actually, hands up any of our readers who are still reading this? On second thoughts, don’t bother. Let’s push on.)
Right, here’s the solution.
But first the map.

Now then…we’ve already established over the last couple of postings the TMB for point ‘D’, which, incidentally, was 4.595 metres above sea level. Unfortunately, the terrain between point ‘D’ and point ‘A’ (the latter of which is the point that we’re trying to obtain a ‘spot level’ for) consists of a steep bank. The sort of bank that dumpy’s can’t see over. Putting the measuring staff on the peg at Point ‘A’ means that there’s no way the dumpy is high enough to read any measurements.
The solution? Put the dumpy over the peg at Point ‘A’ instead, and the measuring staff on the peg at point ‘D’.
Obvious really.

On the off chance that you didn’t quite follow that, here are a couple of diagrams that should help explain matters. Firstly, the wrong way to do it:

Secondly, the right way to do it:

With the dumpy and the measuring staff now in reverse positions, it’s a simple case of taking a reading from the staff and adding it to the height above sea level as recorded by the TBM (or, in this instance, point ‘D’.)
Let’s do that then. According to Ivan and Steve’s calculations, as we’ve already mentioned, point ‘D’ was exactly 4.595 metres above sea level.
The measurement on the staff as viewed through the dumpy was 3.31 metres.
The total height above sea level was, therefore, 7.905 metres.
So the height of point ‘A’ is 7.905 metres above sea level.
Or is it? Anybody spot what we’ve missed? That’s right…we haven’t taken the height of the dumpy itself into account. So, one last measurement of the dumpy then, which on this occasion came to 58 centimetres. Take this away from the total height and you have…7.325 metres…or to put it another way, 7 metres 32 and a half centimetres above sea level.

Okay…did all of that make sense?
I hope it did, because that’s the simplest use of the dumpy that there is.

In future articles (although I can’t promise you when yet) we’ll be covering ‘contour surveys’ and ‘gridding out’, both of which require the surveyor’s level and both of which are absolutely essential when it comes to correct procedures for conducting archaeological surveys. In the meantime, one last photograph of Steve and Ivan on the riverbank at Cockle Hall, with Steve proudly showing off his extended staff…

10 comments:

Ozfemme said...

*looks around to see if anyone has put their hand up*

Brian Hughes said...

I hope not. I wouldn't be able to hear them with all the snoring going on.

John said...

Brian,
All this is very interesting, but hard to grasp in one sit since I keep coming here before my coffee. Trust me... we're all just tired. That's it. The snores have nothing to do with the material.

Just make sure you copyrite this stuff, before some outfit down south decides to publixh it themselves.

Seriously, though, I do hope you are planning to publish a handy little tome of professional behavior for the archeologist. And if so, please add a chapter about keeping an open mind, and especially about fitting the theory to the data, and not vice versa. Some archeologists need to learn that lesson.

Cheers, JOHN :0o

Brian Hughes said...

John,

I wouldn't mind if somebody down south did publish this information. (Tidied up and made a bit more understandable, of course.) It's almost impossible to get comprehensive books on this sort of stuff. Well...it's almost impossible to get them in Fleetwood at any rate. To be honest, if it doesn't have a ripped bodice and some swooning tart in the arms of a gay Victorian male model on the cover, it's impossible to get any book in Fleetwood.

John said...

Oh, pshaw... I'm sure you can get some good books on the subject. We have Discovering Our Past, which covers how to be a respectable archeologist, and was text for a class.

And I ask again, why don't you publish it? You're obviously going to all this trouble presenting the material... surely we cannot assume that all this work is for your gentle readers?

We appreciate it, though, just in case.

Cheers, JOHN :0)

Brian Hughes said...

John,

If we ever compile enough 'How to be an Archaeologist' articles on this board to complete a full book, then we probably will produce one...just for the sake of it. For now, though, we want to keep these postings eclectic if we can, because, after all not everyone wants to be an archaeologist...and the way things are going with Bourne Hill and stuff at the moment, I can't honestly say that I blame them.

John said...

Politics... somehow or other, politics spoils everything, from Bourne Hill to the playground down the street. And if it isn't politics, it's paperwork... usually brought about by lawyers.

So what's the hold up there, now? Can you not get permission for another trench? You said you know exactly where you want to dig next... sounds like you have a hunch about something!

Don't keep us in suspense, unless you have to, to protect the site.

Cheers, JOHN :0)

Brian Hughes said...

John,

Unfortunately it's all very complicated...way too complicated for comments boxes and such like. I know where I'd like to dig on Bourne Hill next...but I can't. I wrote any further involvement with the place off six months ago when the petty politicians got interested.

Feral Beast said...

Thanks for telling me that Brian, I like it how you try to make it simple.

Brian Hughes said...

'Try' being the operative word, Mr. Beast. No matter how many books and articles I've read on 'surveying' they always sound really complicated. When you actually have a go yourself, however, it's not that difficult. Get your Mum and Dad to buy you a dumpy level and you'll see what I mean...