I have the above level but there is no instruction leaflet with it. I have used one before, but many years ago, I need to check that it's working properly. There is a spanner in the leather case that it came in, I imagine it is used to adjust the bubble in order to calibrate it. Can anyone help please? Don
There is a standard method of adjusting a Dumpy level that should be found in every basic guide to surveying.
Or more usefully, it's probably in "Brickwork" vol 3 too, which is worth having and is also on Google books
Thanks for that, Andy. I'm sorry of my reply appeared a little terse, but I was trying to make the point that the Watts level should be adjusted in the same way as any other Dumpy level, using the standard technique that should be widely available online or in basic texts.
Not at all. Merely that it's probably worth many posters to UK DIY buying a cheapish commonplace text on bricklaying, but far fewer of us will get as much benefit from a book on surveying.
It probably _shouldn't_ be adjusted (for most construction instruments) but there will be a procedure for _checking_ it. This checking is necessary, is simpler to carry out, and can be done by muddy-footed numpties in the field. If it needs anything more then breathing on though, let alone serious "adjustment", then someone has dropped it and the whole lot needs to go back to a clean bench indoors for checking.
With a Dumpy there aren't so many degrees of freedom, so it is possible to adjust the collimation of the bubble and the optics relatively safely (i.e. fiddling won't put something else out of whack!). You need two marks that are distant and adjustable to be level, with the level itself moving between them. "Distant" means "within useful range" and "further than the working distance" whilst "level" means "precisely measurable to my acceptable tolerance" but _doesn't_ need to be accurate, as you refine this as you work.
If the level is in adjustment, your marks will appear to be level no matter which end you're sighting from. If your level is inaccurate and you adjust the marks to appear "level" one way, then they'll appear to be out by twice the level's error when you measure from the opposite end. So then point the level's telescope to midway vertically between the two points, adjust the bubble to be "level" again (a bit more accurate this time) and repeat the process end-over-end until the error is no longer measurable.
Oddly I don't own a functional Dumpy level. An old decorative one, a few theodolites, a Cowley, a SiteSquare and the handiest one of all (for practical jobs) which is some Yank hand-held pocket thing with a pinhole rather than an eyepiece and no objective lens other than a stadia graticule.
My nearest thing to a "Dumpy" is a Watts Autoset. It has the weird semi-circular tripod mount so I still don't have a decent tripod for it and it's basically untrustworthy. Anyone with a little nous can check that a Dumpy is behaving itself, but with an Autoset you can never tell for sure unless you trust that the pendulum mechanism is doing what it ought. Any stickiness in there can be very awkward for you, unless it becomes obvious. Some sort of "Incabloc" mechanism would help too.
True enough. Anyway, thanks.
OK, many thanks for the info and advice, following on your comments regarding building books, I remembered that I had a set of "Caxton Modern Practical Building" which I bought many years ago in a market stall for £8, they are the 1950 3rd edition. Although they are no longer "Modern" they still have a lot of practical information which I've found useful in the past. So I looked up Dumpy level and sure enough I found a chapter on surveying & levelling and how to use the dumpy level and more importantly a section on " The causes of error in levelling".
Thanks again
Don.
You're welcome, but I think Andy probably helped more than I did.
I have developed my own methods of setting up and adjusting surveying instruments. They are usually very quick but can be complex.
The traditional, slow and straightforward methods suit the occasional user best, but I have forgotten most of them, which is why I thought it was better to suggest looking them up. It was Andy who suggested looking them up in a building book rather than one on surveying, which is what I had suggested.
;-)
Take it to any Survey Company who perform calibration, usually cost =C2=A320.oo. Google 2 pin test this will indicate how to check and calibrate a dumpy level, the s10 u= ses the same principles except you have to remove 1/2 error on bubble until it remains= central throughout 360 degree rotation =
This instrument has an accuracy of plus or minus 6 mm in contrast to a modern dumpy leve= l accuracy of 2.5 mm. The disadvantage with the Watts level is that on each individual sighting you have to= manually set the leveling bubble. With today's modern Dumpy as long as the instrumen= t remains inside the Bullseye the self leveling compensator will eradicate any leve= ling error and accuracy will be maintained.
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