This is an examination of measurement uncertainty, an important but poorly understood element in any experiment. Emphasis is placed on developing confidence in uncertainty analysis results and using measurement uncertainty in selecting instrument systems. The author traces the steps of complete analysis, including defining the experimental set-up, locating and estimating the magnitude of errors, propagating the errors into the test results, calculating the measurement uncertainty and presenting the uncertainty results. The text is aimed at the college level, and assumes a rudimentary understanding of calculus.