'F' is the symbol of the "degree Fahrenheit", a unit for measuring temperature that originally uses a scale of 32 F for the freezing point of the water and 212 F for boiling. To measure ambient temperature is more practical than the Celsius grade scale in very cold climate countries, where in winter it always drops below 0oC and with this scale should use negative values. Its creator was the Polish physicist Daniel Gabriel Fahrenheit. See kelvin , K , degree Celsius , C .
