Came across this just now whilst looking for a new spirit level:
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like it would be much easier and quicker to read accurately than a bubble, though the 'ball' looks a little vulnerable. Has anyone seen or used one of these in the flesh? 37 quid is a lot to spend if it's a piece of junk.
(As this reads a bit like one of those 'just found this great blah blah blah' spams, I should point out that I actually found it on eBay, item 320427322254, but d+m tools has better pictures, and of course I have nothing to do with either seller)
I cannot believe anyone can read the angular position of a 35-40mm sphere to the same accuracy as a spirit level. A decent level will show the difference of a piece of thin card inserted under the end of a level. So that is about 0.5mm in 600mm - better than
No, it's bollocks. It doesn't have the vernier effect of a long, shallow bubble. These things are _easy_ to read, but far from precise. 5 degrees would be lucky.
If you want accuracy, why not use the device I just invented this minute - a pool of mercury with a metal plate above each end. The capacitance is measured and a row of LEDs light up :)
The local university made a mercury inclinometer (without the LEDs) and noticed that the whole city tilted twice a day because of the tides. Auckland is between two harbours with different tide times.
They may not be idiots, just not as well educated as you!
The H&S police would ban the mercury idea, and interferance fringes may be a tad hard to see in some of the places that I use my spirit level. Monochromatic light source might be tricky on a building site
It is a lot more accurate than 3mm, You don't read top of the meniscus at one end and bottom of meniscus at other. Also in a small tube the meniscus would be a lot less than 3mm.
Don't confuse precision with accuracy. They are two different things.
Some years ago I did a comparison of water level and precise levelling techniques using an optical level and staff. The systematic errors of the two methods were 3mm and 1mm respectively.
The 3mm systematic error for the water level occurred even though users were trained always to read the bottom of the meniscus. Had that not been the case, the systematic error would have been correspondingly higher.
What was good about the water level was that systematic errors remained the same over a wide range of distances. That was very encouraging, and vindicated our choice of water levels to lay concrete ground slabs in a 180 m x 54 m building. Precise levelling using optical methods showed that the slabs as built were well within the tolerance of + or - 5mm stated in the contract.
In such a small tube, viscosity would become a greater problem.
Please don't think I am in any way criticising water levels. They are simple and very effective. Like any method of surveying or measuring, they have their limitations, but when used within those limitations, they are accurate (within 3mm) and supremely reliable. And they don't need highly trained people to operate them.
I assume they don't mean a tube small enough for capillary action to occur.
It needs a bit of training otherwise they will level one end and forget that both ends move when you lift or drop one end. Sometimes with a serious delay.
Do water levels work better if you put detergent in the water?
No, but viscosity would become a problem long before capillary action was an issue.
That's why I emphasised they don't need people to be *highly* trained.
The ones I have used have all had anti-freeze in. perhaps that has the same effect of reducing surface tension? I would not presume to know how best to design one, my experience has been using them together with other methods.
True, I have only ever used them on construction sites except once, when I made one according to "your" design. It worked, but I would not have trusted it to be accurate to any better than ~ 5 mm.
The cheapest laser I have that will show interference fringes in this application is still a He-Ne (30 quid S/H these days, from supermarket scanners). You won't do it usefully with an eBay laser pointer module.
The great advantage though is that it maintains that same precision over varying lengths, up to quite long. I wouldn't use one to put up a bookshelf, but I still prefer it to a Cowley, dumpy or theodolite for general DIY building work.
When quoting my message, you deleted the paragraph:
Why would you delete that, only to make the same comment yourself?
Agreed. I tend to use a Dumpy (actually a Kern) more than most people would because (a) I own one and (b) using one is second nature to me. It's also a bit of a collector's item, a thing of beauty, and I use it whenever I get the chance.
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