Vacuum Gauge/Economy Meter: Description and Operation

Fig. 3 Typical vacuum gauge:

This gauge, Fig. 3, measures intake manifold vacuum. The intake manifold vacuum varies with engine operating conditions, carburetor adjustments, valve timing, ignition timing and general engine condition.
Since the optimum fuel economy is directly proportional to a properly functioning engine, a high vacuum reading on the gauge relates to fuel economy. For this reason some manufacturers call the vacuum gauge a ``Fuel Economy Indicator.'' Most gauges have colored sectors the green sector being the ``Economy'' range and red the ``Power'' range. Therefore, the vehicle should be operated with gauge registering in the green sector or a high numerical number, Fig. 3, for maximum economy.