Functional simulation is the most widely used method for design verification. At various levels of abstraction, e.g., behavioral, register-transfer level and gate level, the designer simulates the design using a large number of vectors attempting to debug and verify the design. A major problem with functional simulation is the lack of good metrics and tools to evaluate the quality of a set of functional vectors. Metrics used currently are based on instruction counts and are quite simplistic. Designers are forced to use ad-hoc methods to terminate functional simulation, e.g., CPU time limitations. We propose a new metric for measuring the extent of design verification provided by a set of functional simulation vectors. This metric is universal, and can be used uniformly for all designs. Our metric computes observability information to determine whether effects of errors that are activated by the program stimuli can be observed at the circuit outputs. We provide preliminary experimental ...