Uncertainty

Uncertainty is a value that characterizes the dispersion of values that could reasonably occur under the test conditions. It is represented with the ± symbol and expressed with only one significant figure.

There are two types of uncertainty: absolute and relative.

Absolute uncertainty is expressed as a constant number. e.g. 10cm ± 1cm

Relative uncertainty is expressed as a percentage of the uncertain number. Relative uncertainty can be calculated by dividing the absolute uncertainty by the uncertain number. e.g. 10cm ± 10%

Addition and Subtraction
When adding or subtracting two values with uncertainties, the absolute uncertainties are added.

e.g. 50cm ± 8cm - 20cm ± 2cm = 30cm ± 30cm

Multiplication and Division
When multiplying or dividing, the relative uncertainties are added.

e.g. 100cm ± 5% / 2cm ± 10% = 50cm ± 15%