The intent of this paper is to explain in simple terms the performance differences between the precision cal component and the InstaCal module. To aid the reader, this paper includes three graphs, one that gives users an easy way to estimate the error based on the measured return loss. The other two graphs compares the return loss measurement of a 3 dB pad and a 20 dB offset using both the InstaCal and OSLN50-1 precision cal components.