A procedure for measuring the status and progress of a complex system development program. The procedure is based on four premises: (1) Progress is characterized by reduction of uncertainty; hence, if uncertainty can be measured at different times, progress can be indicated by changes in measures of uncertainty. (2) Assessment of uncertainty relative to development is subjective. (3) Subjective estimates of uncertainty can be expressed in terms of probabilities. (4) The amount of uncertainty is indicated by statistical measures of appropriate probability distributions. Consistent with these premises, the procedure for obtaining probability distributions for critical system performance characteristics involves five steps: (1) Obtain design equations. (2) Determine subjective probabilities. (3) Generate probability distributions for system performance. (4) Calculate statistical measures. (5) Compare measures at different times to obtain indications of progress. Methods for determining subjective probabilities should be tested in a real-world development program.