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Physical Units on Chart Axes

  1. Oct 12, 2011 #1
    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. jcsd
  3. Oct 12, 2011 #2

    xts

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    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
  4. Oct 12, 2011 #3
    So +1 for []

    It is K.W-1 Temperature rise in Kelvin per unit power Watt
     
  5. Oct 12, 2011 #4

    xts

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

    [itex]\big[{\rm K}/{\rm W}\big][/itex] looks OK for me too.
     
  6. Oct 12, 2011 #5
    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
  7. Oct 12, 2011 #6

    xts

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    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 [itex]h=6.63\cdot 10^{-34}{\rm J}\,{\rm s}[/itex], while NIST recommends to use cross: [itex]h=6.63\times 10^{-34}{\rm J}\cdot {\rm s}[/itex]
    That may be a cause while I don't like dots between units...
    That would be a disaster: [itex]h=6.63\cdot 10^{-34}{\rm kg}\cdot {\rm m}^{2}\cdot {\rm s}^{-1}[/itex]
     
    Last edited: Oct 12, 2011
  8. Oct 12, 2011 #7
    Yes it does, agreed!
     
  9. Oct 12, 2011 #8

    sophiecentaur

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    Science Advisor
    Gold Member

    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..
     
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