Medical thermometer and displaying temperature became available, electronic thermometers (often called "digital", because they display numeric values) have been used. Many display readings to great precision (0.1 °C or 0.2 °F, sometimes half that), but this should not be taken as a guarantee of accuracy: specified accuracy must be checked in documentation and maintained by periodical recalibration. A typical inexpensive electronic ear thermometer for home use has a displayed resolution of 0.1 °C, but a stated accuracy within ±0.2 °C (±0.35 °F) when new. The first electronic clinical thermometer, invented in 1954, used a flexible probe that contained a Carboloy thermistor. Types
Mercury-in-glass thermometer Nowadays, the triple point of water is used instead of the freezing point (the triple point occurs at 273.16 kelvins (K), 0.01 °C). Before the discovery of the true thermodynamic temperature, the thermometer "defined" the temperature; thermometers made with different materials would define different temperature scales (a coloured alcohol thermometer would give a slightly different reading than a mercury thermometer at, say half-scale). In practice, several materials gave very similar temperatures to each other and, when discovered, to the thermodynamic temperature. One special kind of mercury-in-glass thermometer, called a maximum thermometer, works by having a constriction in the neck close