Whether contact or non-contact measurement of temperature is performed, all thermometers have an uncertainty associated with the measurements they perform.
The relevant ISO standard for clinical thermometry stipulates that a clinical temperature measurement device must have a measurement uncertainty associated with the device of not greater than to ± 0.3 °C (k = 2) when manufactured.
There are however, a number of other factors which over time can impact this measurement uncertainty, for example:
- Drifts in the electronics of the thermometer over time
- A shock to the device, such as dropping or extended exposure to a strong heat source
- Prolonged use without performance confirmation