calibrating an old analytical balance

[leaf12]

I have an old Mettler HL32 analytical balance and I want to calibrate it. I've unsuccesfully looked for any info on this kind of balances on the net and TFSE.

I have measured out 20,00 mL of dH2O, the weight was 19,87 g. Not so good anymore.

Below are some pictures. Does anyone know the functions of the several switches? Where can the RS232-like connection be used for?

I guess the CAL switch is to calibrate, but is this only to set the whole thing to absolute zero? Because I want to recalibrate it with calibration weights.

Thanks for any info!!

[Osmium]

> I've unsuccesfully looked for any info on this kind of balances on
> the net and TFSE.

Then send an email to the manufacturer, I have repeatedly received manuals for free.

> I have measured out 20,00 mL of dH2O,

How?

> the weight was 19,87 g. Not so good anymore.

The density of water at 20°C is 0.99821g/ml. But liquids aren't suitable calibration standards.

> Where can the RS232-like connection be used for?

That looks like a parallel printer port.

> I guess the CAL switch is to calibrate, but is this only to set
> the whole thing to absolute zero? Because I want to recalibrate
> it with calibration weights.

I assume the calibration is done with a certain weight (e.g. 20.000g), and the switch is used to tell the device that this weight is actually 20.000g instead the 19.998g the balance reports. Some of those toys even have their own calibration weight built in. Get the manual from the manufacturer.

The whole calibration thing might be unnecessary, assuming you really managed to put exactly 20ml of water on that balance (which I doubt) and the reported weight was 19.87 instead of the true 19.96whatever grams then it's off by less than 0.5% which is good enough for most purposes.

[livid]

I've seen manuals for this type of stuff at online auctions,some I think are for sale. post your own add, that your looking for one

[Ed_]

There were calibration weights being sold on Ebay before.  Don't buy any unless they give the specs.

Go here

http://www.ebay.com

and put in keywords like "calibration weight"

[_mu_]

If it ain't broken, don't fix it.

If you measure out 20 ml of water, and get 19.87 grams, you can assume linearity of at least. 1%. This assumes you get 9.9 grams when you measure out 10 ml of water. So what is 1% error in 10-80 mg of psychoactive compound?

BTW, as osmium already pointed out, you can't use water (or any other liquid) to calibrate your balance. Getting an exact volume out, right down to the microliter is *hard*. Plus, if you weigh it, you'll see your calibration altering continously because of evaporation and all that stuff.

You almost sound like you're desperate to tweak. Please don't. Chances are, the thing is as good as it is, and you won't make it better.