Laser levels

I got a screwfix catalogue last week that offered some levels by Forge Steel. They have a self levelling one for 37 49 and a Rotary one for the same price. Yet the bumph says that they are both self levelling.
Both are class II whatever that means, the first has a 10 m range whilst the rotary has a 30 m range. So what are the likely differences anyone know?
http://www.screwfix.com/search.do ;jsessionid=GQZRDX4X0CABOCSTHZOCFEY?_dyncharset=UTF-8&fh_search=Forge+Steel+Level&x=8&y=11
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If you load the instruction manual for the rotary the accuracy which is quoted in +/- mm per m is 1 which seems an awful lot. At 5m you are going to be 5 mm out (possibly)
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Most fixed levels are accurate to around 1mm in 1000mm so not really any different.
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Stanley SP5 +- 0.2mm per m
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Lurch wrote:

A slight difference being that if you were transferring a level a long distance with a conventional level, then you would (well should!) reverse it each time you extend the level - that way you reverse out any error each time. With a laser level you would not do this, so the base accuracy needs to be better really.
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The spec. in the booklet is 0.15 degrees per metre. That isn't a great deal of inaccuracy.With the rotary one the range is 30 metres so the inaccuracy -if it remains at 0.15 degrees per metre over the full range, is 4.5 degrees.
But if I had to ever use it on a 60 metre room I should feel entitled to ask my employer to hire an expensive one. Also at that range the two end readings would be the same error and the same level.
Moving the laser to the mid points, between the centre of the building and its two ends, would allow me to take the correct reading from the centre of the building and correct each end reading in turn.
At 40 quid that's not a bad bargain. I think that hiring a good one for a day costs more than that.
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wrote:

degrees per metre? Strange units
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Except in the very largest of rooms, the beam does not curve.
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|!>> Lurch wrote: |!>> >>>http://www.screwfix.com/search.do ;jsessionid=GQZRDX4X0CABOCSTHZOCFEY?... |!>> >> If you load the instruction manual for the rotary the accuracy which |!>> >> is quoted in +/- mm per m is 1 which seems an awful lot. At 5m you are |!>> >> going to be 5 mm out (possibly) |!>> |!>> > Most fixed levels are accurate to around 1mm in 1000mm so not really |!>> > any different. |!>> |!>> A slight difference being that if you were transferring a level a long |!>> distance with a conventional level, then you would (well should!) |!>> reverse it each time you extend the level - that way you reverse out any |!>> error each time. With a laser level you would not do this, so the base |!>> accuracy needs to be better really. |!> |!> The spec. in the booklet is 0.15 degrees per metre. That isn't a great |!> deal of inaccuracy.With the rotary one the range is 30 metres so the |!> inaccuracy -if it remains at 0.15 degrees per metre over the full |!> range, is 4.5 degrees. |! |!Except in the very largest of rooms, the beam does not curve.
All beams curve *a little* even when the load is only the weight of the beam itself. This may be very little, indeed not measurable with DIY tools.
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Dave Fawthrop <dave hyphenologist co uk> Compare and contrast
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wrote:

woooosh
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On Tue, 27 Feb 2007 07:16:42 +0000, Dave Fawthrop

Of course they do.
Now what's the weight of _this_ beam?
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On 25 Feb 2007 19:01:05 -0800, "Weatherlawyer"

There are two sorts: line generators and flying spot rotaries.
Line generators have a lens system that projects a line. Usually it has two of them, at right angles. Rotaries have a single whirling mirror that projects a single spot quickly enough to look constant. For much more money you can also find twin spot rotaries.
They're both self levelling, owing to a pendulum. Usually line generators are much more accomodating of tilt.
Both have an apparent brightness that varies with the angle of the surface they shine on, so the "centre" of the projected line is usually brightest and it tails off to the sides. The line generators are also significantly brighter in the centre of the line, so their side performance is relatively poor. Spot brightness is effectively independent of range, until its diameter gets bigger -- it's the side slant direction that limits their use, not the straight-on spot.
So for indoor use, such as tiling, get a line generator. They're cheap and wonderful
For other uses, you ought to get a rotary, but you can't afford it (still 200+). Cheapie rotaries are neither one thing nor the other.
The tripods are all far too short and basically worthless. You need an adapter (cheap from a camera shop) to use them on a photographic tripod.
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Thanks for all that Andrew.
I can afford but would seldom use a 200 level. I might get a line generator one day. But for getting door frames all on the same level I just use a block of wood on the floor.(Unless I am following obvious incompetents.)
It's just that with the modern insulated floors that are getting specified these days, it might be an idea. As I work on sites, it doesn't approach my requirements that I supply any such a thing.
I've only needed to use one once and the firm hired it. It was rather expensive to hire one. If I was doing a lot of studding it would be a different matter.
It is interesting to learn what these things do though, as to a layman they all seem much of a muchness.
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