# Which is a more accurate scale for a chemistry high school lab - a triple beam balance or a digital balance and why?

I would like to ask the experts of this chemistry community their opinions on which balance is more accurate and effective to use in a high school chemistry lab- a triple beam balance or a digital balance. I would appreciate your rationales for your answers as well. Thanks!

• I would say digital scales would be more robust, what is needed in high school environment. Aug 3, 2021 at 5:24
• on the other hand, making people use a beam balance will surely teach them more. Aug 3, 2021 at 12:21
• Consider a different perspective, seen e.g., in mechanical or civil engineering: what are the specifications the device in question must fulfill to be good enough; what is a nice have, or irrelevant? Note these parameters e.g., what is the accuracy yo need in the experiments ahead, then look out for a balance. Aug 3, 2021 at 14:36
• Having used a triple beam and chain weights in college, I doubt a modern HS student could reliably handle them. Aug 3, 2021 at 18:34
• Orthogonal suggestion: The United States penny weighs 2.5 grams; the nickel, 5 grams. Along with UK coinage, sub-gram accuracy can be achieved using a simple balance and a modest investment of under 20 USD. I haven't explored completely, but I suspect milligram tolerance can be achieved with US and UK coins alone. Add coinage from other countries and you're all set. Aug 3, 2021 at 23:54

A digital balance is much easier to use. I guarantee some of your HS students are going to have huge errors when using a triple beam because they don't know how to read it. That's not necessarily a downside—you might want to give them training in the skill of using and reading a mechanical balance. OTOH, if you want them to focus on other aspects of the lab, or are concerned about time constraints, then a digital balance (which can be used much more quickly) would be the way to go.

As far as accuracy goes, at the entry level for calibrated quality scales (~\$150), you can get a digital balance with NIST-traceable calibration and the following specs (Cole-Parmer Symmetry Compact Portable Toploading Balance, 300g x 0.01g): Triple beam balances typically only have 0.1 g readability. To get 0.01 g readability in a beam balance, you'd need to add finer adjustment, with either a dial or an extra beam. These get pricer (~$250+). Here's a quadruple-beam balance with 0.1 g readability, though without specs for repeatability or linearity: Ohaus 311-00 Cent-O-Gram Overhead Mechanical Balance, 311g x 0.01g.

But for a HS lab, you'll probably want to spend more like \$30/scale. There the only way to determine the relative accuracy of the triple beam and digital balances will be to buy a set of calibrated weights and check for yourself. [Regardless of what claim the vendors make.] [And note that there will probably be a lot of inter-unit variation at that cost level, where some will be much more linear than others.]

• Calibrating a balance with standard weights is irrelevant, if the actual weights used by the students are contaminated and/or corroded by who knows what. Of course contamination may occur during a student's experiment, so it is not even a systematic measuring error. Aug 3, 2021 at 15:07
• "Calibrating a balance with standard weights is irrelevant", no it is not. It is a norm. First, because students don't calibrate balances. It is done by a certified technician annually or a qualified teacher and there is an elaborate procedure to do it. Standard weights are highly protected so the chances of contamination is very low. Aug 3, 2021 at 15:50

Recall that Theodore W. Richards got a Nobel Prize on "in recognition of his accurate determinations of the atomic weight of a large number of chemical elements." Guess which year was that? 1914!! Digital balances did not exist then. All high accuracy balances were mechanical balances then.

The point is that you can have a very crappy digital balance or a triple beam balance (= low price, no certification). All the accuracy of balances depends on their calibration with known weights. The accuracy of those known weights, depends on how they were calibrated by national and international standardizing agencies.

It all depends on the purpose. For organic synthesis work, a triple beam balance would be fine where ultrahigh accuracy of measured weight is not a big deal. What is being weighed and what is the level of accuracy required? How many accurate digits are required?

In short, both digital and triple beam balances are fine for routine work. We cannot say one is more accurate than the other. After all, the digital balance is also requires mechanical movement (i.e., it also has moving parts which you cannot see).

• I would say durability is more important than accuracy in high school lab context( and the former affects the latter during the time too) . :-) I remember in my high school days in 1980-84 that our very classical mechanical scales were frequently out of order. Students are the ultimate realization of the Murphy's law saying even things that you cannot imagine be broken can be broken. Aug 3, 2021 at 7:07
• I have not said digital ones would survive. I have just said they may survive longer. :-) Aug 3, 2021 at 17:18
• The worst part is trying not to drop the calibrated weights on the floor… Ive experienced even expensive digital scales going out of calibration just in a few days. Learned the importance of checking them daily.
– user98623
Aug 3, 2021 at 17:42
• In pharma, I was told that they calibrate balances daily. No chances for any mistakes. Aug 3, 2021 at 17:44
• @M.Farooq yes we do… every morning
– user98623
Aug 3, 2021 at 17:47