Here in Germany you’ll see “kmh” as often as “km/h”, and it usually pronounced “ka-em-ha” (not “ka-em-pro-ha” or “ka-em-strich-ha”).

In English, it should, in theory, be either “km/h” or “kmph” (the p replacing the /, like in “mph”). However, you just as often see “kmh”.

As for saying it out loud, the problem is that, like it or not, “miles an hour” rolls more smoothly off the tongue than does “kilometres an hour” (whether you stress the ‘i’ or the ‘o’), which, to my ears, is all the more reason for allowing “kay-em-(h)aitch”.

The DfT (well, it’s predecessor) have recognised for many years that “m” isn’t being used correctly but still choose to do nothing about it.

For more information, please visit the BIPM website. The entire SI brouchure can be accessed from www.bipm.org/en/publications/. Rules regarding the use of upper and lower case letters can be found in Chapter 5 of the brochure.

My own preference is to use lower case if there is a prefix (eg 100 ml), but to use upper case if there is no prefix (eg 5 L).

I know what ‘ and ” are supposed to mean… I was merely pointing out that their normal use in the UK is much more confusing than the continuing use of “m = mile”.

To be brutally honest, from the viewpoint of getting metric used here in the UK I am quite happy to tolerate “T” for tonnes or KM where km should be used (outside of “official” signage and documentation) because at least it means that somebody is trying. I just can’t abide the fact that a government department who admitted that “m” and “M” shouldn’t be used for miles 18 years ago has done nothing to fix it - and it almost looks intentional!

(Oh… and I work for an American IT company and have spent some time in North America so have had much experience of the # - which interestingly occupies the same key on a US keyboard as the British £ does on the UK keyboard!)

‘ means minutes as applied to angles and ” means seconds as applied to angles.

Did you know that in the US the number symbol # is called a pound sign and is suppose to mean pounds of weight. As in handwritten signs showing the weight of goods using this symbol.

Tomatoes: $1.99 #

On a telephone, an automatic operator may cue you to use the “pound sign”, meaning the # symbol after entering numbers.

Unit symbols make more sense on distance signs, for two reasons:

1) Distance signs come in many different shapes, therefore adding “km” to a number clarifies that this is a distance (rather than a road number, exit number, etc.).

2) While speed limits fall roughly within a single decade (20-200 km/h), distances posted on road signs can cover at least five decades (5-500000 m). A unit symbol helps here to resolve any ambiguity that might remain.