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Significant figures and uncertainty

  1. Apr 8, 2012 #1
    Let’s say I have a class A 25ml pipet with an uncertainty of +/- 0.24ml.

    If I want to express the volume of the pipet to the correct number of sig figs to say determine the sig figs in a final answer - what is it?

    Is it 25 ie two, because that is the marking?

    Or 25.00 ie four, because the uncertainty limits the range to 24.76 – 25.24, which are 4 sig fig values?

    Or 25.0 ie three, being 0.24 rounded down to the nearest single sig fig?

  2. jcsd
  3. Apr 9, 2012 #2


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    Welcome to PF!

    Hi Miffymycat! Welcome to PF! :smile:
    Technically that's 2 significant figures.

    (though I'd be tempted to call it 2.5 significant figures, since it obviously could be rounded to the nearest 1/2 ml)

    I'd be inclined to call it ±1%, and wait and see what the final answer is …

    if it's say 89.4, then make it 89 (2 sig figs) since that's ±1%

    if it's say 11.4, then make it 11.4 (3 sig figs) since that's ±1%.

    if it's say 33.4, then i dunno … judgment call! :confused:

    What do other people think? :smile:
  4. Apr 9, 2012 #3


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    Re: Welcome to PF!

    SF are faulty by design?
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