Abstract: A system for monitoring the rotational velocity of a shaft. The system includes a shaft pulse generator, an off-delay circuit and on-delay circuit. The sensor provides a series of pulses having an instantaneous repetition rate proportional to the rotational velocity of a shaft. The off-delay circuit includes a retriggerable multivibrator. In response to each pulse in the series of pulses, the multivibrator switches to a first binary state if in a second binary state at the time of an applied pulse, or remains in the first binary state if in that state at the time of the applied pulse. The multivibrator is further responsive to the most recent pulse in the series to switch from its first binary state to its second binary state a first predetermined period after the most recent pulse. The multivibrator provides a state signal representative of its current state.