A method for calibrating a thermometer is provided. The method includes deriving values of at least two different reference calibration coefficients of a reference calibration equation. The reference calibration equation relates temperature of a reference temperature sensor to at least two different calibration coefficients and a measured characteristic of the reference temperature sensor. A primary temperature sensor of the thermometer is calibrated using the derived values of the at least two different reference calibration coefficients. In another method for calibrating a thermometer, value of at least one reference calibration coefficient is derived from a reference calibration equation. The reference calibration equation is a non-linear equation relating the temperature of the reference temperature sensor to the at least one calibration coefficient and a measured characteristic of the reference temperature sensor.