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smile.gif posted on 23-12-2011 at 16:20
Calibration Help!


Good News- Tomorrow my family and I celebrate Christmas and I am about 95% sure that my family got me an Ohaus SPE-123 milligram balance.

Bad News- I now have the knowledge that Ohaus doesn't include the weight with the balance. :( I would refuse to operate a nice expensive milligram balance unless it is accurate and precise within a milligram!


I'd like to know if there is any good ghetto way to calibrate a balance to hold me over until I can get a weight. Is there anything you find that always equalls 100 grams? My original idea was to get paper and cut a piece that weighs 100g, but... that would be a lot of paper. I also know US nickels weigh 5g, but it can differ depending how used they are. I also considered calibrating with 100mL of water, but I can't tare the mass of the beaker (and my 100mL volumetric flask is cheap...)...

Any ideas that can actually work? Thnks in advance! :)




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Mr. Wizard
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[*] posted on 23-12-2011 at 16:50


You could ask a high school or college lab to weigh an item your bring in, such as a nickel dime, quarter and half dollar. Clean the coins before you bring them in so it won't be contaminated with perspiration and oils. Handle them with clean plastic tongs after cleaning. Keep the 'standards' in a dry plastic container with the actual weights marked on the container. Plan B would be to buy some standards.
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MagicJigPipe
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[*] posted on 23-12-2011 at 21:22


I'm jealous. No one in my family would ever have the ... for lack of a better term ... "knowhow" to select such an instrument for me.

Or, now that I've looked it up, the money!

There's nothing you're going to find that will give you exact weights down to the milligram (other than standards, of course). Even lightly used nickels (still bright and shiney, from 2011) seem to vary by at least a few tenths of a milligram to a couple of milligrams. That didn't make sense to me but, unless the balance I was using was crap, which is possible, it is supported by actual measurements.

Even if you could make accurate water measurements down to the microliter, this wouldn't be reliable as the purity of the water would effect the density (not to mention the temperature to a smaller extent). Just use nickels for now. It will be close enough for most things (unless you're making drugs and ingesting them I guess; and even then...).





"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think, free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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grndpndr
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[*] posted on 24-12-2011 at 02:03


If you know a fella who reloads for his firearms,the projectiles (bullets) he uses are likely quite accurately made wieghed/consistent.If you could get hold of match grade bullet(s) the accuracy would be to the grain.Also most major US manufacturers hold thier std grade of firearms projectiles to within a few grains.IIRC a box of 100 std grade
Rifle bullets varyed by no more than 2-3 grains with the very careful or anal reloader seperating them by wieght.
Recall 1gram is equivalent to 15.43 grains.In fact I used to/still do, use my reloading scale to measue subgram wieghts as most
powder/reloading scales are accurate to a grain.

Sounds like youll have a nice present from Santa.Merry Christmas

[Edited on 24-12-2011 by grndpndr]
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Dr.Bob
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[*] posted on 24-12-2011 at 09:04


Paper would be a bad choice, as it absorbs humidity from the air and changes weight constantly. It is fine for comparing paper areas, like for GC, where there is a relative weight needed, but for an absolute reference, paper would not work well. Even a simple paper label for a 4 ml vial will change weight by up to 1 mg with a change in humidity.

You should find a large metal object or two, weight it on a fine balance somewhere else (or even two of them, which will show you how much even good balances can vary) and then record that weight. That should be fine for a reference. Some items about 10 grams and 100 grams are good starting points, and you can find them with the new balance. I have also seen calibration weight sets for sale at many places, both new and used, including at coin shops.
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[*] posted on 24-12-2011 at 10:09


Think I could take it to a gun or jewelry store and ask them to calibrate it for me? But then it suffers changes the ride home... I hate gravity...



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[*] posted on 25-12-2011 at 08:50


Well, luckily my scale came with a calibration weight. It is a wonderful scale- highly reccomend it for anyone who still uses those decigram drug dealer scales (like I used up till... um... yesterday!). The draft shield works great. It is very professional, but has a cute and modern design.:)

Lolz... I have to post some nerd porn of it... :)

Now I can officially brag that I have one of the best scales on this forum (Although I am behind that one member that has that 0.00001 g balance... who was that?).lolz, I won't brag... that is rude... But if you want a good price for this scale, my parents ordered it from ITIN SCALE, in NY.

Merry Christmas, everyone!




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MagicJigPipe
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[*] posted on 25-12-2011 at 14:34


That's great. I wouldn't say it is the best scale on the forum. Many of us have analytical balances which typically have precisions of no less than +/- 0.0002 g. (these things, when new, are thousands of dollars).

Still, you have a nice gift there. Take care of it.

A 1984 U.S. Nickel:

U.S. Nickel (1984).jpg - 40kB

It's dark and flash doesn't work well and I didn't feel like spending a bunch of time on the "perfect shot". But, that's to give you an idea of how much is "rubbed off" of a nickel after 27-28 years. Not much, huh?

Find a 1984 nickel and see what your balance says... I'm curious.




"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think, free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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[*] posted on 26-12-2011 at 11:37


Mine shows 5.010, but it could be minor differences in the coin and where it was minted at.



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franklyn
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[*] posted on 26-12-2011 at 14:51


A trick that is useful ( after you have accurately calibrated your scale ) is to weigh
the scale itself by placing it upside down on a pedestal near the edge of a table to
read the result from underneath. Thereafter this will provide a bench mark you can
always use , providing that the same brand of batteries are used.

- Official coin weights -
http://www.usmint.gov/faqs/circulating_coins/index.cfm?flash...

- Observations found online regarding coins ,

the PENNY weighs 2.5 gm , four new ones accurately weigh 10 gm.
the NICKEL weighs 5.0 gm, 20 new ones accurately weigh 100 gm.

since there are 453.6 gm/ lb

182 pennies ($1.82) are 455 gm (~ pound )

91 NICKELS ( $4.55)(1.0 gm/ cent ) are 455 gm (~ pound )


DIMES, QUARTERS, 1/2 DOLLARS are all worth $20/ lb


" A nickel can weight from between 4.9 and 5.1 grams (weighed a bunch) (heard of
4.8 to 4.85 but only was able to replicate with heavily used nickels or thousands
decimal place scales even then bout 70 percent of the time they were between
4.9 and 5.1) (depends on the wear, if you wanted to do a real locked down test
you could go to the bank and get a fresh from the press new roll of nickels or
pennies for that matter) If your scale weights within that range I would say the
scale is accurate to the hundredths decimal place."

.
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[*] posted on 6-1-2012 at 04:20


Perhaps you could weigh a pie to calibrate it, somewhere over the rainbow. Nice gift btw, and to think of all the other possible gifts you could have been granted in its stead, such as a huge pillow made of feathers, a really huge pillow.



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