The TQC Magnetic Thermometer measures surface temperature. The thermometer can easily be placed on ferrous substrates with the strong magnet on the back. Surface temperature can be read out in both °C and °F. Measuring Range is -10°C to + 70°C; +14°F to +60 °F. The diameter of the thermometer is 65 mm. Can be used in vacuum. No plastic parts on the outside of the thermometer.