Cdeg and Fdeg are used for temperature <i>differences</i>, e.g. a difference of 5 Celsius (Cdeg) is equivalent to 9 Fahrenheit (Fdeg) (and to 5 Kelvin of course).
About the display, 0=B0C is stored internally in K (-273.15). In single precision, the closest number that can represent this is about -273,14999390 so that's why 0=B0C isn't exactly 0. Just change the format and precision (2 digits floating point) to display 0.00.
