REAL multiplicative calibration factor; it is used to convert from the sin- gle dish map units (e.g., main-beam brightness temperature) to janskys. A default value of 0 can be used if the original data file is in unit of Tmb, the main beam brightness temperature, because in this case the conver- sion factor can be derived from the beam size. UV_SHORT will complain if it cannot derive the appropriate value.