Basic Thermometry Concepts: Resolution
Resolution refers to the smallest detectable increment of measurement on an instrument. A thermometer that displays temperature readings to the hundredth of a degree (e.g. 100.26°) has a greater resolution than one that only shows the tenths of a degree (e.g. 100.3°) or whole degrees (100°).
Although resolution is different than accuracy, the two should be thought of as going hand in hand. After all, a thermometer that is accurate to ±0.05° wouldn't be half has useful if its resolution were only in tenths of a degree (e.g. 0.1°). Likewise, it could be misleading for a thermometer to show hundredths of a degree on its display, if it's traceable accuracy were only ±1°.
Sometimes the resolution of a given thermometer changes above or below a certain temperature. The ThermoWorks Precision Plus Thermometer, for example, has a resolution of 0.01° up to 199.9°F and a resolution of 0.1° above 199.9°F all the way up to its upper range specification (1562.0°F [850.0°C]). A thermometer that automatically adjusts its resolution at the critical temperature, like the Precision Plus, is said to be "auto-ranging."
In rare cases, the resolution of a thermometer can be affected by the limitations of its digital display—older thermometer models often only had space to display three digits, so even though the thermometer and probe were precise to the tenth of a degree, after 99.9° or -99.9°, only whole digits were displayed (i.e. 100° or -100°).