# Uncertainty Calculations

1. Feb 8, 2009

### jgens

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?

Thanks!

2. Feb 8, 2009

### dlgoff

Check out this http://en.wikipedia.org/wiki/Significant_figures" [Broken]

Last edited by a moderator: May 4, 2017
3. Feb 8, 2009

### jgens

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?

4. Feb 8, 2009

### 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.

5. Feb 9, 2009

### cesiumfrog

You're correct. If your experiment has uncertainty of tens of centimetres, then report your result to tens of centimetres.