<div class="htmlview paragraph">Mixture strength, or equivalence ratio, is the primary factor affecting the fuel consumption and exhaust emissions of a gasoline engine. A new instrument has recently been developed to monitor equivalence ratio. The response time of the instrument is 1/2 second, so that the effects of engine transient conditions, such as fast throttle opening, can be studied with greater accuracy than is possible with current exhaust emission analysers.</div> <div class="htmlview paragraph">This paper will cover the concept, design and development of the prototype instrument, including the calibration tests on gas mixtures and an engine. In addition, a more sophisticated meter has been designed for production. The equivalence ratio characteristics of a number of current and advanced engines have been monitored with this instrument and the results are presented.</div>