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Measurement Problem

by Quarlep
Tags: lenght, measurement
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Quarlep
#1
Feb16-14, 01:54 AM
P: 71
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
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Seydlitz
#2
Feb16-14, 03:10 AM
Seydlitz's Avatar
P: 255
Quote Quote by Quarlep View Post
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
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.
Nugatory
#3
Feb16-14, 04:33 AM
Sci Advisor
Thanks
P: 3,654
Quote Quote by Quarlep View Post
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
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

nmf77
#4
Feb16-14, 07:55 AM
P: 13
Measurement Problem

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!
Mark44
#5
Feb16-14, 11:33 AM
Mentor
P: 21,255
Quote Quote by Quarlep View Post
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
Quote Quote by Seydlitz View Post
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.
As Nugatory points out, the error portion is ##\pm## 0.05. Also, the units involved are centimeters, not kilometers

Quote Quote by Nugatory View Post
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
Quarlep, the measurement is between 1.95 cm and 2.05 cm.


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