City-Data Forum Is it considered "wrong" to use square brackets around units during calculations? (chemistry, physics)
 User Name Remember Me Password [Register]
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.

06-02-2019, 03:47 AM
 170 posts, read 66,510 times Reputation: 97

I have a vague memory that a teacher once commented on me using square brackets around units on an old exam paper (not totally sure if that's correct, but I seem to remember something like that), and I also think I have read something about this on a few Internet sites.

I was wondering exactly why this is considered wrong?
I think that square brackets are very handy because they clearly show what it is that's supposed to be units, and this minimises confusion (assuming of course that the square brackets aren't expected to have any other use in those claculations), so I was wondering why this would be wrong, other than because it's not "convention" to do it that way?
Square brackets even make it easier for myself as well, because they eliminate the risks that I will mistake a unit for a variable and things like that.
I usually treat units exactly like variables, since that feels more natural to me, so the square bracket notation is very handy to me for that reason, since it's not always clear if something is written in slanted notation or not ("m" vs. "m", for example).

06-02-2019, 09:57 AM
 4,956 posts, read 2,243,666 times Reputation: 14207
Well, I am not exactly sure what you're asking about, but I won't let that stop me.

If you're talking about writing "seventy-five kilograms per meter" as 75[kg/m] I would say that's kind of strange. Normal notation would just be 75 kg/m.

I don't know what you mean by "slanted notation" (italic?). If you are writing something by hand there is absolutely no way on earth you can distinguish between italic and not-italic, it is purely something for typeset documents or things handwritten in blackletter (which I'm sure you're not doing for math or science calculations). In manuscript the convention used to be that things to be typeset in italics were underlined.

If that comment relates to the difficulty in telling the difference between variables and units, then I would simply say not to use the same letters of the alphabet for units as for variables. Of course if you are doing any calculation of mass, you are stuck and you'll just have to figure out how to deal with it. But obviously you're going to get in trouble if you treat "meters" as a variable in a calculation dealing with mass where mass is a quantity to be found.

As far as "treating units exactly like variables" I think you need to read up on dimensional analysis. I am not qualified to explain it adequately here, though I use the principles all the time. I think you have got hold of a partial version of this, but I fear you don't have a complete understanding of it.

06-02-2019, 10:51 PM
 Location: Pacific 🌉 °N, 🌄°W 11,038 posts, read 4,773,027 times Reputation: 7060
Quote:
 Originally Posted by Markus86 I have a vague memory that a teacher once commented on me using square brackets around units on an old exam paper (not totally sure if that's correct, but I seem to remember something like that), and I also think I have read something about this on a few Internet sites. I was wondering exactly why this is considered wrong? I think that square brackets are very handy because they clearly show what it is that's supposed to be units, and this minimises confusion (assuming of course that the square brackets aren't expected to have any other use in those claculations), so I was wondering why this would be wrong, other than because it's not "convention" to do it that way? Square brackets even make it easier for myself as well, because they eliminate the risks that I will mistake a unit for a variable and things like that. I usually treat units exactly like variables, since that feels more natural to me, so the square bracket notation is very handy to me for that reason, since it's not always clear if something is written in slanted notation or not ("m" vs. "m", for example).
Hi Markus86,

Just out of curiosity I wanted to ask the following:

What is your major if you're in college?

I find many of your questions to be unusual for a person taking science/math courses...especially if you're in college.

And here's a video:

When Do You Use a Bracket and a Parenthesis in Math?

06-03-2019, 10:04 PM
 170 posts, read 66,510 times Reputation: 97
Well the point is that I feel that square brackets emphasise when something is supposed to be a unit instead of a variable, and I always point this out very clearly whenever I do it during exams.
And so far I haven't got any points deducted because of this, but only comments like "don't use square brackets", as far as I can remember.
But really, why not?
As long as I clearly point out how I use them, then what's the actual problem?
It doesn't affect the calculations in any way and it doesn't violate any mathematical rules, it just makes it easier to see what it is that's supposed to be units.
It's really just another version of how some books write units in a red colour (like Chemistrył, for example).

I study Engineering Physics at university.

Last edited by Markus86; 06-03-2019 at 10:35 PM..

06-04-2019, 07:05 AM
 4,956 posts, read 2,243,666 times Reputation: 14207
Well, there are a zillion different notations for the same thing, oftentimes. My advice would be that while you are in school you use whatever notation is preferred by each instructor. When you are on the job you can use whatever is comfortable for you.

Some examples: using the "dot" notation for derivatives - much beloved of some people, I hate it because it doesn't tell you what it's differentiated with respect to. I prefer dy/dx notation. If y and x are position and time is t, dy/dx can be very very different from dy/dt. Just putting "y dot" doesn't provide enough information, in my opinion.

Vectors - I have seen at least five or six different schemes for distinguishing vectors from scalars, in my university days.

Heck, we can't even agree on the square root of -1. To mathematicians it's i, but to EEs that's specific current and the square root of -1 is j.

Again, notations are created by people to allow them to understand things. In school, use the notation the professor or the book uses, to minimize the chance of miscommunication. On the job, use whatever works for you - and, if you're going to communicate your calculations to someone else, make sure to provide a key.

06-06-2019, 12:53 PM
 Location: Seattle 523 posts, read 132,159 times Reputation: 545
Square brackets are often used to distinguish additions by a commentator that weren't in the original statement. (E.g. [sic].) Perhaps that can prove confusing to some?

06-10-2019, 05:24 AM
 3,673 posts, read 3,077,379 times Reputation: 7713
Quote:
 Originally Posted by turf3 Again, notations are created by people to allow them to understand things. In school, use the notation the professor or the book uses, to minimize the chance of miscommunication. On the job, use whatever works for you - and, if you're going to communicate your calculations to someone else, make sure to provide a key.
Bingo. There is little upside in trying to win over a professor to your unique system even if it's superior.
 Please register to post and access all features of our very popular forum. It is free and quick. Over \$68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned. Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.