a lot of guys say their air/fuel gauges are usesless - they just bounce around. They suggest that if you want one for "looks" go for it, but for practicality, save your money. I have 2 5/8 electric oil pressure, mechanical water temp (as noted above), and then a vacuum gauge. Vacuum gauges could be used to get decent fuel economy - try to keep as much vacuum as possible and you'll have the best mpg (vacuum is really close to 0 at Wide-Open Throttle).