1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Uncertainty Calculations

  1. Feb 8, 2009 #1


    User Avatar
    Gold Member

    My physics teacher said that our resultant answer should have the same number of sig. figs. as our uncertainty (he allows 2 sig. figs. at most); however, having done some of the problems, I get answers - when not rounded - such as 24.0 +- 0.1m, which when rounded to 1 sig. fig. results in 20 +- 0.1m which is not even near the minimum possible value. Did he perhaps mean to say the same number of decimal places?

  2. jcsd
  3. Feb 8, 2009 #2


    User Avatar
    Science Advisor
    Gold Member

    Check out this http://en.wikipedia.org/wiki/Significant_figures" [Broken]
    Last edited by a moderator: May 4, 2017
  4. Feb 8, 2009 #3


    User Avatar
    Gold Member

    Having read the wikipedia page, I still don't think I have an answer. 24.0 has three sig. figs. while 0.1 has only one; therefore, if I round to 1 sig. fig. like my teacher said - result should have as many sig. figs. as uncertainty - I would get 20 +- 0.1. Is this correct?
  5. Feb 8, 2009 #4


    User Avatar

    Staff: Mentor

    The simplified rule of thumb for uncertainties is:

    When you add or subtract, round the final result to the least number of decimal places.

    When you multiply or divide, round the final result to the least number of significant figures.
  6. Feb 9, 2009 #5
    You're correct. If your experiment has uncertainty of tens of centimetres, then report your result to tens of centimetres.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Uncertainty Calculations