Physical Units on Chart Axes

1. Oct 12, 2011

pow216

Hello,

Just wondered what the correct way is to display physical units on chart axes.

Let's say for example thermal resistance of a heatsink extrusion is plotted as a function of length, and so the units for the y-axis are K.W-1

My 'A' Level physics teacher always insisted on (in order that the axes was dimensionless):-
/K.W-1
My previous boss insisted on round brackets
(K.W-1)
and I've seen square brackets in some scientific computing applications
[K.W-1]

Whats the consensus?

Thanks people.

2. Oct 12, 2011

xts

I think the convention varies from country to country - I often see () in Russian texts.
I used to use [] in my texts (English, Polish, German) and never got it corrected by redactors.
I use () instead of [] if the natural language description is used rather than symbols, e.g.: (arbitrary units)

BTW: what is K.W-1??? Shouldn't it be kW-1 ?

Last edited: Oct 12, 2011
3. Oct 12, 2011

pow216

So +1 for []

It is K.W-1 Temperature rise in Kelvin per unit power Watt

4. Oct 12, 2011

xts

I would never use the dot, just a thinspace: $\big[{\rm K}\,\,{\rm W}^{-1}\big]$ rather than $\big[{\rm K}\cdot {\rm W}^{-1}\big]$ or $\big[{\rm KW}^{-1}\big]$

$\big[{\rm K}/{\rm W}\big]$ looks OK for me too.

5. Oct 12, 2011

pow216

Interesting I have long been under the impression that dots were correct, have a look at #5 here:-

http://physics.nist.gov/cuu/Units/checklist.html" [Broken]

Last edited by a moderator: May 5, 2017
6. Oct 12, 2011

xts

It says that both dots and thinspaces are equally valid.
As I noticed - the conventions may vary from country to country - the guide you cite is American one.
I learnt such conventions in Poland and Germany - here dots are rarely used, they smell for me with 'primary-school-pedantry'.

BTW - I see one more difference between conventions I used to and those recommended by NIST.
I always type $h=6.63\cdot 10^{-34}{\rm J}\,{\rm s}$, while NIST recommends to use cross: $h=6.63\times 10^{-34}{\rm J}\cdot {\rm s}$
That may be a cause while I don't like dots between units...
That would be a disaster: $h=6.63\cdot 10^{-34}{\rm kg}\cdot {\rm m}^{2}\cdot {\rm s}^{-1}$

Last edited: Oct 12, 2011
7. Oct 12, 2011

pow216

Yes it does, agreed!

8. Oct 12, 2011

sophiecentaur

The dimensionless option gets my vote.
The oblique ( / slash?) slash needs to be there because the label would, strictly, be W-1K but that could easily confuse a chap.
In (bog standard) algebra, one doesn't use a multiplication symbol between letters, so I should say that a dot is superfluous unless there is an actual 'dot product' involved..