Uncertainty

Absolute uncertainty

Half the smallest interval
1 sf
Reading must be to the same degree of accuracy

Instrument	Interval size	Reading
Meter rule	$0.1 \unit{cm}$	$50.55\pm0.05 \unit{cm}$
Protractor	$1 \degree$	$34.0\pm0.5 \degree$
Voltmeter	$1 \unit{V}$	$6.0\pm0.5 \unit{V}$

If $a$ is the quantity,
$\Delta a$ is the absolute uncertainty

Fractional & percentage uncertainty

\begin{align*} \text{fractional uncertainty} &= \frac{\Delta a}{a} \\ \text{percentage uncertainty} &= \frac{\Delta a}{a} \cdot 100\% \end{align*}

Calculating uncertainties

Addition/subtraction - add the absolute uncertainties
Multiplication/division - add the fractional/percentage uncertainties
Power/root - multiply the fractional/percentage uncertainty by the power