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There is an uncertainty in every measurement we take, known as the instrumental uncertainty. This uncertainty depends on the measuring device and should be included in every table, and with any data referenced. There are two categories of instrumental uncertainty: analogue and digital.
Analogue Instrumental Uncertainty
This is half the smallest division of the measuring device.
This is 10 V with an uncertainty of 0.5 V. This is recorded as:
10.0 ± 0.5 V
The precision of the uncertainty gives the precision of the actual value.
Other analogue examples could include a measuring cylinder, thermometer:
60.0 ±0.5 mL
and
23 ± 2 °C
Rulers - the occasional exception
A meter ruler is an analogue device, but there is a measurement at two ends. We do not want to discuss propagation of uncertainties here so I will simply state that this means we add the two uncertainties together. In the example below the ruler has a smallest division of 1 mm, so the uncertainty is 0.5 mm. However, because there are two points that are being measured, and therefore two uncertainties, we double the uncertainty to be 1 mm.
Digital Instrumental Uncertainty
This is the smallest division of the measuring device.
This is 0.12 A with an uncertainty of 0.01 A. This is recorded as:
0.12 ± 0.01 A
The precision of the uncertainty gives the precision of the actual value.
Other digital examples could include a multi-meter and voltmeter:
1.09 ±0.01 V
and
9.12 ± 0.01 V
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