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!

Measurement Problem

  1. Feb 16, 2014 #1
    Hi I saw something in Wikipedia and I am confused. I saw something like this
    2.0 cm -/+ 0.05 cm Whats that mean?
    My first opinion Between 1,5 and 2,5
    My second opinion 1,5 cm or 2,5 cm
  2. jcsd
  3. Feb 16, 2014 #2
    It means the error is between the value written after -/+, so for example 1.0 km -/+ 0.5 km. That means we are not certain that the measurement is 1.0 km as given by whatever instruments we have. The real value can range between 1.5 km and 0.5 km.
  4. Feb 16, 2014 #3


    User Avatar

    Staff: Mentor

    Your first thought ("between") is right, but have you dropped a decimal place in there? ##2.0{\pm}0.05## means between 1.95 and 2.05, not 1.5 and 2.5
  5. Feb 16, 2014 #4
    I think of the +/- as the uncertainty in the measurement in a statistical sense. This may be a subtlety different view to that posted above. I don't interpret those bounds as definitely encompassing the 'true measurement'. Usually I'd take it to mean that there's a 68% chance (1 sigma) that the true measurement is in that range, assuming 'normal' statistics of course. Just my view, others may disagree!
  6. Feb 16, 2014 #5


    Staff: Mentor

    As Nugatory points out, the error portion is ##\pm## 0.05. Also, the units involved are centimeters, not kilometers

    Quarlep, the measurement is between 1.95 cm and 2.05 cm.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook