By John Brennan | Updated Mar 24, 2022
Photo by Jay_Zynism via iStock/GettyImages
Every temperature measurement carries a degree of uncertainty. Whether you’re using a digital probe or a classic mercury tube, the instrument’s precision and your observation method determine how tightly you can pin down a value.
Place the thermometer’s sensing element against the object whose temperature you wish to record.
For digital devices, watch the display while it stabilizes. If the reading oscillates, the uncertainty equals the full range of the fluctuation. For example, a temperature that swings between 20.12 °C and 20.18 °C has an uncertainty of ±0.06 °C.
If the digital display remains steady, treat the final digit as the uncertain element. A reading of 36.12 °C therefore carries an uncertainty of ±0.01 °C, reflecting the precision of the last place.
When using a mercury or alcohol column, estimate the temperature to the nearest mark you can discern. Reading to the nearest 0.1 °C yields an uncertainty of ±0.1 °C; if you can only read to the nearest 0.5 °C, the uncertainty expands to ±0.5 °C. The key is to match the uncertainty to the instrument’s resolution.
