Bob,
Another useful resource for AFR meters is at
http://wbo2.com/ . I have built
a couple of their units, one is fitted in the 412 later to be interfaced to
a megasquirt unit (I`ve built a couple of these as well) which will control
a sequential gas injection system.
Useful thing with the wbO2 is that it can take inputs from other sensors,
(rpm, throttle position, etc.) and store the data. This can be read out at a
later time, so you can see exactly how your engine is performing under road
conditions.
John P