Following the previous article about the limited impact of UKMA’s Metric Style Guide and the widespread mistakes in writing metric symbols, we look at one major source of these mistakes. Too many avoid the use of awkward characters that cannot be found on a standard keyboard and end up writing metric symbols incorrectly.
Here are common mistakes that writers make for some common measurements:
| Measurement | Common Mistake | Correct Metric Symbol |
|---|---|---|
| degrees Celsius | C  | °C  |
| micrograms | mcg | µg |
| grams per square metre | gsm, GSM | g/m² |
| square metres | sq m, sqm, SQM | m² |
| square kilometres | sq km, SQ KM | km² |
| cubic centimetres | cc, CC | cm³ |
| cubic metres | cu m, CU M | m³ |
The first two metric symbols contain characters that cannot easily be found on a standard keyboard. The other metric symbols in the list can either be written with a standard digit formatted as superscript or as a special character for squared or cubed.
The other common mistake is the failure to leave a space between the number and the metric symbol. Could this be caused by the difficulties of producing a non-breaking space on a standard keyboard? A non-breaking space ensures that the number and metric symbol are not split by a line break, unlike a standard space.
These mistakes are commonly found in the media, on signs, in advertising and on product labels.
On Windows PCs and laptops, you can use the Character Map to select and copy characters that do not have their own keys. The Character Map can be accessed from the Start menu. Depending on your version of Windows, you can search for it by typing “character” then choosing Character Map from the results or you can look for it under Accessories or Windows Accessories folder in the Start menu. Here is the Character Map with the °, µ, ², ³ and non-breaking space characters used for metric symbols inside red boxes in the image below:
The mappings for these characters are shown in the following table:
| Glyph | Character Description | Unicode Code Point | Keystroke |
|---|---|---|---|
| No-Break Space | U+00A0 | Alt+0160 | |
| ° | Degree Sign | U+00B0 | Alt+0176 |
| ² | Superscript Two | U+00B2 | Alt+0178 |
| ³ | Superscript Three | U+00B3 | Alt+0179 |
| µ | Micro Sign | U+00B5 | Alt+0181 |
You can select and copy these characters using the Character Map then paste them into your document. Or you can press the Alt key, enter the symbol’s 4-digit code on the number keypad then release the Alt key to type the respective character directly into your document.
I suspect that too many writers and journalists find it too hard to produce these characters, so they prefer to take the easy way out and write their own language-dependent abbreviations. This is lazy and metrologically illiterate. The media need to make more effort to write metric symbols correctly. We should make a start to improve matters in our schools. This needs to be taught in schools where correct metric symbol usage should be an essential part of the measurements section of mathematics education. It is clear that more needs to be done to improve the situation.
Metric Views 
A very good article. I liked the term ‘metrologically illiterate’.
Writers and journalists should read it.
+=+=+
And for the bit about schools; NOT just mathematics, all subjects. For example: how many geography teachers use ‘sq km’? How many home economics/cooking teachers still have ‘cc’ in their hand-outs? And these of course, instead of using cm³ – could use mL for millilitre.
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In the course of my working life, I came across, many times, the need for a non-breaking space in various circumstances, in the course of producing many technical and training documents. The copy that authors produce is seldom in its final form. It is subsequently processed to fit the columns of the final publication. That means word-wrapping takes place as column width changes from the original. Words wrap where a space occurs near the end of a line. Hence the need for the non-break space. It would not do, for the quantity to end a line and the symbol to begin the next line.
In Microsoft Office, the easiest way to produce a non-breaking space is by holding down the SHIFT and CTRL keys simultaneously and tapping the space key. This is only slightly more difficulty than producing a regular space. However, it does not work outside MS Office, as far as I am aware. The method using the character map, or the ALT key and the numeric keypad (if available), does work everywhere.
The problem is that hardware design does not make it easy to be correct. Many reporters produce their copy on laptop computers, many of which have more-restricted keyboards and no numerical keypad. I submitted a letter to the Institution of Engineering and Technology on this subject several years ago.
Why is the space in front of the symbol important, anyway? This is a point that I have seen specified, have adhered to myself, but never seen explained anywhere. I presume it is because, particularly if the numerical quantity ends with a 0 or 1, the absence of the space blurs the distinction between the quantity and the symbol – letters and numerals become confused and it can even look like a strange word. The is the point that I have promoted in the past, anyway; does anyone have a better reason? It seems that many authors do not see this problem as frequent enough to be important, and avoiding the space avoids the risk of a line break in an inappropriate place.
A simple solution would be a minor redesign of the mechanical keyboard layout. The space key is unnecessarily wide. Split it, and make the right side the regular space and the left side the non-break space. Unfortunately, at present neither ANSI nor ISO seems interested in making this a keyboard standard. Hence, many authors, often working under pressure, take the easy option. I would suggest that the dated and cluttered practice of using a comma as thousands separator in numbers persists for the same reason.
I agree with Martin Vlietstra’s points. With a new keyboard layout standardized, we could then enhance the way that the keyboard is mapped. Just as the SHIFT key effectively gives each other key an alternative character, so another key, e.g., the ALT key, could provide a third character, e.g., from the Greek character set. I am sure that keyboard drivers could be designed to do this. Give people the tools to do easily what we want them to do.
I don’t think the answer is in tackling the teaching in schools. I have no reason to believe that schools are teaching wrongly. But the points here are:
• Schools teach ideology, not practice.
• School children have no influence in how the world of work operates.
• School leavers are expected to conform with the practices of the work places they enter.
When I was at school, maths and science teachers taught us that “m” was the symbol for metre, and the symbol for mile was “mi”. Sixty-plus, years on, the DFT still has not caught up with this idea.
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Metricmac asked, “Why is the space in front of the symbol important, anyway?”
I think the best explanation for this is given in the SI brochure:
“5.4.3 Formatting the value of a quantity
The numerical value always precedes the unit and a space is always used to separate the unit from the number. Thus the value of the quantity is the product of the number and the unit. The space between the number and the unit is regarded as a multiplication sign (just as a space between units implies multiplication).”
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Thanks, m, for your extract from the SI brochure. However, I don’t find the brochure information very convincing, and I don’t think writers and journalists are convinced either, if they have read this.
In my dealings with maths, if algebraic symbols are concatenated without spaces, they are regarded as multiplied together. Otherwise, multiplication is expressed by an operator symbol between the characters, e.g. a dot – or raised dot nowadays. (The x symbol is deprecated because it can be confused with the very common algebraic symbol for the unknown quantity.)
Furthermore, I am stretching my imagination to see the expression of a quantity followed by a symbol as a multiplying operation. It is the specification of the size of the quantity that the symbol represents. Most people would not regard “12 apples” as “12 multiplied by apples”, would they!
I know that the SI brochure is supposed to be our “bible”, but it is not perfect. I’ll continue to put the space before the symbol nevertheless.
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There is an easier way, at least in MS Word, to generate a non-breaking space: Ctrl+Shift+!
Nice idea to extend the Alt Gr (“Alternate Graphic”) set, although I would put the non-breaking space in the corner of the space bar itself. I guess both keyboard manufacturers and standards bodies would be easier to persuade if we could muster international support, at least from English-speaking countries. Definitely ambitious!
The easier way, at least in MS Word, to generate a non-breaking space bears repeating: Ctrl+Shift+!
Nice idea to extend the Alt Gr (“Alternate Graphic”) set, although I would put the non-breaking space in the corner of the space bar itself. I guess both keyboard manufacturers and standards bodies would be easier to persuade if we could muster international support, at least from English-speaking countries. Definitely ambitious!
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