Sulaiman
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Where to get a PRECISION 1m rule
My plans for a primary reference mercury manometer & barometer are progressing,
I now need a ruler/measure that I can be sure is accurate to 0.1mm in 760mm ....
Looking at eBay I could not find a ruler with the guaranteed accuracy required,
any ideas ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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NedsHead
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For that level of accuracy you might want to look at getting a machinist height gauge, they can be purchased as vernier or digital type
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aga
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Steel engineering rules are good.
As NedsHead says, a digital vernier caliper would be the best tool for the job tho, and they are dirt cheap.
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Sulaiman
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I only need 1mm or 0.5mm precision rulings as I can make vernier scales
BUT
the ABSOLUTE accuracy of markings needs to be within 0.1mm
the cheapest I have found so far is £345 for a 1m vernier caliper
http://www.ebay.co.uk/itm/LARGE-HEAVY-DUTY-VERNIER-CALIPER-M...
very nice but an order of magnitude too expensive !
(I can buy a used Fortin barometer with mercury for £330)
This project is progressing as most of my projects ...
seems easy until I actually start 
EDIT: just two borosilicate tubes, joined at the bottom,
add mercury, apply vacuum andor pressure,
measure the height between each meniscus,
apply corrections for temperature effects
... easily done ... NOT !
I guess I'll just lash it up using a common steel ruler and live with approx. +/- 1 mm Hg accuracy,
good enough for my chemistry needs, not what I wanted though.
EDIT: the seller of the £345 calipers just responded:
"these are marked as 0.02mm / 0.001"
these come with no calibration certification, although we can get it done at additional £70 + vat for the 1 metre vernier "
[Edited on 5-10-2016 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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NedsHead
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you could buy a cheap 6" vernier caliper and scribe your own graduations on a piece of steel
[Edited on 5-10-2016 by NedsHead]
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Sulaiman
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I have a couple of cheap 150mm digital calipers (eBay <£10 each, one for home, one for work)
they agree with each other very well
but is 100.00 mm on the digital scale equal to 100.00 mm ? ... I have doubts
e.g. I have four eBay (cheap Chinese) 100g M2 callibration weights from different suppliers,
they all measure the same to within +/- 0.02g, (0.01g precision scales)
but what do they actually weigh ?
But now that you mention it, I will measure my 1m steel rule using the 150mm calipers,
if agreement is close enough then I'll jut use the steel rule.
P.S. my concern arises from checking various rulers against each other ... some are terribly inaccurate (>1mm)
EDIT:
I set my calipers to100.00 mm and measured the ruler in 100 mm increments,
to the limits of my eyesight and thickness of rulings ... BANG ON !!!!
quest over for now ... THANKS
[Edited on 5-10-2016 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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Tsjerk
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Why don't you make HD photos of any ruler, 1mm precise, next to what you want to measure, do that three times and then use imageJ to see what the
value actually is?
If you zoom in far enough you should be able to determine were the level of your liquid is compared to the 1mm lines on the ruler. If you do this
three times and average I would say that that is a good estimate.
I think that without possible ways to actually measure what you want to measure, these kinds of approaches are usually used in science.
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careysub
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If you buy a precision steel rule made by any reputable machine tool company: Mitutoyo, Starret, Incra, Shinwa, Brown & Sharp, PEC, etc. etc. I
can guarantee you they will be precise to within the limits of your vision (0.1 mm) because they could not sell them if they weren't since their
market is professional machinists and their stock-in-trade is precision tools.
Such a 12" rule can be had for less than $20.
Also, if you have two measuring tools that both agree that 100.00 mm is 100.00 mm, then unless you are suspecting that they have exactly the
same systematic error then they prove each others accuracy. The theory that they agree but are inaccurate would be an extremely improbable one.
Measuring systems that agree precisely, but are yet inaccurate (typically due to dependence on some common calibration source or measurement
transformation factor that is in error) do exist and are encountered in science, but length measuring tools do not fit this bill.
Weight measuring is subject to this sort of error if you don't correct for the local gravity field, which varies by 0.7% over the surface of the Earth
(Arctic Ocean to the mountains of Peru), but otherwise no. Within Europe (outside of Russia) the gravity field varies with latitude by 0.29%, and by
altitude by 0.15% (but not many people are doing chemistry on Mont Blanc). The greatest variation by altitude likely to be encountered would be 0.049%
between sea level and the high altitude town of Davos.
[Edited on 5-10-2016 by careysub]
[Edited on 5-10-2016 by careysub]
About that which we cannot speak, we must remain silent.
-Wittgenstein
Some things can never be spoken
Some things cannot be pronounced
That word does not exist in any language
It will never be uttered by a human mouth
- The Talking Heads
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Tsjerk
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Isn't the problem that the range to measure is 760 mm?
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careysub
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Shouldn't be a big problem. There are a few ways to skin that cat.
One is to simply use one 12" rule (to keep cost down), have reference marks for one of three positions, and move the rule to the region where readings
are being taken. Glue magnets to the back if needed (since most precision rules are stainless steel).
Another is to buy three of these rules and construct a continuous reading system either by placing them on alternate sides, or end to end - precision
rules typically read end-to-end.
About that which we cannot speak, we must remain silent.
-Wittgenstein
Some things can never be spoken
Some things cannot be pronounced
That word does not exist in any language
It will never be uttered by a human mouth
- The Talking Heads
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