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When writing technical emails, it's quite common for me to need to include simple mathematical formulas. I find it hard to clearly include subtractions because dashes are so commonly used as generic word separators. For example,

  • ...amount of widgets (total widgets this month – some other value) will be...

is a lot less clear than if there's an addition or multiplication, simply because of the symbols being used:

  • ...amount of widgets (total widgets this month + some other value) will be...
  • ...amount of widgets (total widgets this month * some other value) will be...

Is there a better or standard way of making it clear that a dash should be treated as a subtraction?

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    Why would someone read an asterisk as a × symbol? Are you writing FORTRAN or English? The case for using - to mean − suggests that you must be. :) Would you expect to use ÷ or / for division?
    – tchrist ♦
    Aug 10, 2022 at 12:14
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    You could write "x-y, where x is the total widgets this month, and y is some other value" or set it off distinctively formatted as an equation (which MS Word's "Insert an Equation", various mathematical markup systems, and other software can do) but Weather Vane's answer is definitely the one I would recommend.
    – Stuart F
    Aug 10, 2022 at 12:43
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    @tchrist: It's not uncommon for both the sender and receiver of a technical email to be very comfortable with using asterisk as a multiplication symbol. It's used in a lot more computer languages (from Excel to C-family languages to many others). Similarly, it's not uncommon to see a caret (^) used for exponentiation (1.8*10^12 is 18 followed by 9 zeros), even though that's not typically used in computer languages (at least the ones I use)
    – Flydog57
    Aug 11, 2022 at 16:24
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    @DarrelHoffman Although of course even non-technical people would probably understand a slash as a fraction if it was in context... "3/4 cup flour"
    – user3067860
    Aug 11, 2022 at 22:52
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    Why would you use a dash (–) to denote subtraction? Use a minus sign! Here’s a free one: ‘−’.
    – user3840170
    Aug 12, 2022 at 18:42

4 Answers 4

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The mathematical symbol - rarely appears between words, because of the likelihood of being misunderstood.

If it has some spacing it could be taken as an en dash

amount of widgets (total widgets this month – some other value)

If it has no spacing it could be taken as a hyphen

amount of widgets (total widgets this month-some other value)

For clarity use the actual word minus

amount of widgets (total widgets this month minus some other value)

For the other examples which the OP claims are clear:

The * symbol only means 'multiply' in computer code, in arithmetic an × is used. When used in text, * usually directs to a footnote.

amount of widgets (total widgets this month multiplied by some other value)

For clarity and consistency, you can similarly spell out the +

amount of widgets (total widgets this month plus some other value)

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – tchrist ♦
    Aug 12, 2022 at 18:43
  • - is not a mathematical symbol. −, however, is.
    – user3840170
    Aug 13, 2022 at 18:44
  • Sorry, I can't tell the difference. All the nit-picks have been moved to chat, if you care to follow them.
    – Weather Vane
    Aug 13, 2022 at 18:45
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I'm going to present a slight frame challenge. Symbols such as -, +, ×, ÷ are best used in formulas, since the context makes their meaning clearer.

If you're using prose, I'd suggest phrases such as "the difference between total widget count this month and last month," or "the sum of total widget and contraption counts," or "the product of hours worked and the number of people working," etc.

This is largely my opinion. I did find a mathematical style guide from Virginia Commonwealth University with this advice (p. 2):

Avoid misuse of symbols. Symbols such as =, ≤, ⊆, ∈, etc. are not words. While it is appropriate to use them in mathematical expressions, they are out of place in other contexts.

The Chicago Manual of Style (16th edition) gives different guidance (p. 581):

Words versus symbols in text. In general mathematical symbols may be used in text in lieu of words, and such statements as "x ≥ 0" should not be rewritten as "x is greater than or equal to zero." Nonetheless, symbols should not be used as a shorthand for words if the result is awkward or ungrammatical.

Personally, I feel like Chicago may be presenting a false dichotomy. Merely substituting the phrase "greater than or equal to" for the symbol ≥ can sound amateurish. Same for a mechanical replacement of the minus sign with the word "minus." There are more prosodic expressions such as "x is at least zero" that could be used instead.

Which takes me back to the frame challenge: If the meaning of the minus sign could be confused with a hyphen, then consider use of plain prose. Don't feel like you must translate your phrase word-for-word, merely substituting the word "minus" for the minus sign. For example, instead of trying to substitute the minus sign directly, you might express your first example as "The number of widgets remaining after accounting for theft..." or something similar.

Finally, if you are intent on using formulas because you feel they capture a complex relationship succinctly, then don't go half-way. Use actual formulas. Something like:

A = B - C

Where:

  • A is the number of widgets we have on hand
  • B is the number of widgets we purchased from Acme on April 7.
  • C is the number of widgets lost to theft or that failed quality-assurance tests.

Or at least make it clear that you are specifying an equation by using an equals sign and putting the equation on a line by itself:

(Amount of Widgets) = (Total Widgets purchased) - (Widgets Lost)

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  • "greater than or equal to" sounds awkward because we already have a perfectly good phrase--"at least".
    – user3067860
    Aug 11, 2022 at 22:52
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    I would add the request to use the actual Unicode math operators instead of ASCII characters that look like them.
    – WGroleau
    Aug 12, 2022 at 5:24
  • @user3067860 .... But "greater than or equal to" is standard in English-language mathematics.
    – GEdgar
    Aug 13, 2022 at 0:53
  • @GEdgar "at least" is fine mathematical language, too. "at least one prime divisor" or "the number of prime divisors is greater than or equal to one"?
    – user3067860
    Aug 13, 2022 at 19:06
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One alternative (probably contrary to style guides) could be to write

net widgets ( = (total widgets) - (widget loss) )

That is, introduce the "math part" by an unequivocal math symbol, available on most current keyboards, and group the words with parentheses. Also, using an asterisk for multiplication may not be the prettiest way, but, especially if introduced with an equals sign, will be understood by many people.

"Less than or equal to" is hard to read, and "at most" also requires a little parsing, in comparison to symbols, assuming the latter are available. Sure, more dignified in some regards... maybe it depends on your relationship to your audience.

Many mail clients "even in 2022" do not cope reliably with unicode, or TeX, or MathML, or ... so using common symbols has some virtues.

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  • This is definitely the way to go. We’re talking about e-mail here, not a typeset document. E-mails are often forwarded and read on platforms without the fancy character sets.
    – user205876
    Aug 13, 2022 at 0:46
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Make it clearer that you are writing a formula by replacing english phrases with something that looks like a pseudocode variable. Use an ordinary ASCII hyphen; its Unicode name is HYPHEN-MINUS for a reason :)

...amount of widgets (total_widgets_this_month - some_other_value) will be...

...amount of widgets (totalWidgetsThisMonth - someOtherValue) will be...

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