My guess is that display routines (that display a number in an indicator) are DBL regardless of the type of the control. For 0 degC(SGL) the displayed value -6,10352E-6 is the result of 273.15(DBL) - 273.15(SGL)
The internal value 273.15(SGL) is probably promoted to DBL with single precision (zero padding in the mantissa) and the is substracted 273.15(DBL) for display, resulting -6,10352E-6.
