Measuring receivers like the 8902A have been used for many years for calibrating attenuators and signal generators. Recent advances in measuring receiver design using digital signal processing tech- niques have made it possible to reduce overall measurement uncer- tainty. However, a rigorous analy- sis of the sources of uncertainty in a complex piece of test equipment requires intimate knowledge of the inner workings of the instrument. ISO 17025 requires knowledge of internal parameters and distribu- tions, which most users do not have. This paper will develop the N5530S measuring receiver uncer- tainty model and guide the reader through several typical measure- ment uncertainty examples.