A tachometer interface circuit is provided for use with a multi-functional measuring device. The tachometer interface circuit includes a conditioning circuit which receives a series of ignition pulses from an internal combustion engine. The conditioning circuit converts the series of ignition pulses into a series of output pulses each having a constant pulse width. The tachometer interface circuit further includes a magnitude sensing circuit and an offset circuit. The magnitude sensing circuit senses the magnitude of the ignition pulses and activates the offset circuit when the magnitude exceeds a predetermined limit. Upon activation, the offset circuit inserts a resistor into the conditioning circuit to reduce the magnitude of the ignition pulses entering the conditioning circuit. In this manner, the tachometer interface circuit of the present invention is able to operate with ignition pulses having a variety of magnitudes.

A monostable multivibrator including trigger circuitry therefor comprising monostable multivibrator means having a normally conducting control element and a normally non-conducting control element, trigger means including means responsive to the positive-going transitions in an input signal for controlling at least one of said control elements to switch the monostable multivibrator means to its unstable state for a predetermined length of time; and the trigger means including means responsive to the negative-going transitions in the input signal for controlling the other of the control elements to again switch the monostable multivibrator to its unstable state for the predetermined length of time; whereby the circuitry may multiply the frequency of the input signal at the output of the monostable multivibrator means.