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Quantitative measures of self-checking power are defined for evaluation, comparison, and design of self-checking circuits. The self-testing and fault-secure properties have the corresponding quantitative measures testing input fraction (TIF), and secure input fraction (SIF). Averaging these measures over the fault set yields basic figures of merit. These simple averages can conceal faults with low values of TIF or SIF. Improved figures of merit, based on geometric means, are defined to provide greater sensitivity to low TIF or SIF. As a demonstration, self-checking linear feedback shift registers (LFR's) based on duplication and serial parity prediction are evaluated.