Guys: My $0.02 Today in lab,I used balances that ranged in price from $6000+ to $89 The $89 balances were centigram balances with accuracy to 0.1 g, capacity of 250 grams. I will not belabor the differences between accuracy and precision - I do it all the time with students that should know better.
However, if a balance has a possible error of 1% for values between 1 gram and 100 grams - than it doesn't matter if you measure out large amounts or small amounts. 1% of 100g is one gram - will not matter for the mix and if you need 10 grams, 1% of 10 grams is 0.1g - well within the tolerance for hardner, etc. or even 2%! Triple beam balances are not as good as a digital balance. The TB balance must be able to swing freely and stop on the zero or the same place each time. If you've used the balance once it is not as good as it was. (I go back to using a "chain-o-matic" analytical balance, same priciple as a TB and those weighing may have taken 30 - 40 minutes, and the standards I had to use, cost me over $100 in 1963) The "use" (and repeated use) of the TB balance rounds off the once sharp fulcrum - and then it will not stop swinging at the same place with the same amount of epoxy, etc or the calibrated set, both accuracy and precision are poor. This fact of life will make them less accurate/precise than the cheapest digital. Forget any rough handling, abuse in shipping, or on the flea market table I've had students check (a lab designed to show students the differences between accuracy and precision with multiple measuring instruments)triple beams against cheap digital - and the cheap digital always wins. Taring on a triple beam is not easy nor quick. Weighing on a TB is not quick either. ALL digital balances will tare with a push of the tare button, so you can use "used" cups, different sized cups, etc. Unless you buy a good set of calibrated masses and DO NOT touch them with anything except clean forceps, they are useless as a calibration standard. Just the oil on your hands (never mind dust and corrosion) will make them worst than the cheapest digital balances. BTW: sometimes you can get really good digital balances at the police station for nothing or a small donation to their fund - they confiscate them in drug busts! Jim Ealy Jim Ealy Education by Demonstration RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
