Abstract: A first thermometer is conventionally calibrated and a second is calibrated to read a predetermined temperature lower than actual temperature and provided with a heater resistor in good heat transfer relation to its bulb. Switch means connects a battery to the resistor to heat the second thermometer until it is observed to read the same as the first. Then the switch is repositioned such that appropriate circuitry causes reduced heating such that the elevated temperature condition of the second thermometer is merely "held" at that position and the bulb of the second thermometer is exposed to the wind and after a predetermined time (on the order of 30 seconds) the second thermometer is read, its reading representing the effective temperature as the result of wind chill.