We mounted a GTechPro Expandable Gauge System (EGS) tach on my orange Chevelle. This tach offers an analog and a digital readout on the same screen. We have it currently set up to display the A/F ratio (using an Innovate LC-1 sensor) and rpm. Note how the display indicates a very lean 19.4:1 A/F at 855 rpm idle in gear. This is not a truly accurate indication because of free oxygen trapped in the exhaust gas due to massive cam overlap.