Sensitivity criteria are reviewed and concisely formulated in terms of system flowgraphs. Formulas are developed for the sensitivity of a terminated two-port, if subject to variations of wide range of parameters, and the results are tabulated. The effectiveness of sensitivity calculations is demonstrated through numerous examples such as the voltage sensitivity of a regulated power supply. Other examples include a probabilistic model of failure modes in reliability. The techniques are thus extended to systems with predictable rather than measurable, parameters. The flowgraph approach provides 1) insight into system operation, 2) facilitates sensitivity calculations and 3) establishes a systematic approach to assess the effects of parameter variations.