Scales & Balances

["James Purchase" <jppurchase at rogers_com>]

Back in February of 2001, Chuck Gadd was wondering about how he could obtain
more accuracy in dosing certain nutrients. In response to his question,
Roger Miller wrote the following:

"The best procedure is to get (beg/borrow/buy) a reasonably accurate
scale and measure the weight and volume of the chemicals you use under
your conditions.  That isn't a real satisfying alternative for most
people, but I think it's the only solution that will make your
calculations reasonably accurate."

O.K., I don't have access to a University/Research Lab with an analytical
balance, but I do have a web browser and a credit card (oh no, not the
credit card again!). I've been considering buying a balance and from
searching the web, it seems that my choice is to get either a mechanical
beam balance or a digital scale, probably one designed for use by jewellers
(small size and precision).

I have narrowed down the search to the following models:
Mechanical -
Ohaus Triple Beam, capacity of 610 g with a sensitivity of 0.1 g
Ohaus Cent-O-Gram, capacity of 310 g with a sensitivity of 0.01 g
Digital -
iBalance 101, capacity of 100 g with a sensitivity of 0.01 g
MyWeight MX-50, capacity of 50 g with a sensitivity of 0.01 g
MyWeight Flipscale 125, capacity of 125 g with a sensitivity of 0.05 g
MyWeight Flipscale 350, capacity of 350 g with a sensitivity of 0.1 g

Now, to my questions - does anyone have any opinions as to the relative
accuracy of a mechanical balance such as either of the Ohaus models and a
small digital balance. Is one to be preferred over the other on the basis of
absolute accuracy?

- how much precision is required? Is a sensitivity of 0.1 g enough or should
I pop for a model that can read to 0.01 g?

I'm REALLY tired of tablespoons, teaspoons, etc. and would like to know what
I'm putting into my tanks with more precision.

Thanks,

James Purchase
Toronto