[Donwill]

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

[Bruce[_4_]]

"Donwill" popple @diddle .dot wrote:
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?


There is a standard method of adjusting a Dumpy level that should be
found in every basic guide to surveying.

[Andy Dingley]

On 2 Mar, 12:51, Bruce wrote:

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
http://books.google.co.uk/books?id=i...fox-a#PPA83,M1

I was trying to set up a SiteSquare the other day and was pleasantly
surprised to find that the web's best effort then turned out to be
this book, which was already on the shelf within arm's reach - I'd
forgotten it did optics too.

[Bruce[_4_]]

Andy Dingley wrote:
On 2 Mar, 12:51, Bruce wrote:

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
http://books.google.co.uk/books?id=i...fox-a#PPA83,M1

I was trying to set up a SiteSquare the other day and was pleasantly
surprised to find that the web's best effort then turned out to be
this book, which was already on the shelf within arm's reach - I'd
forgotten it did optics too.


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.

[Andy Dingley]

On 2 Mar, 15:42, Bruce wrote:

I'm sorry of my reply appeared a little terse,

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.

but I was trying to make the point that the Watts level should be
adjusted

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.


in the same way as any other Dumpy level,

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.

[Bruce[_4_]]

Andy Dingley wrote:

On 2 Mar, 15:42, Bruce wrote:

I'm sorry of my reply appeared a little terse,

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.


True enough. Anyway, thanks.

[Donwill]

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.

[Bruce[_4_]]

"Donwill" popple @diddle .dot wrote:
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


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.

;-)

[Pat Lang]

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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