[mstngjoe]

Here is a graph that allows you convert you CO readings to A/F ratio. The emissions stations here in Oregon will run older cars that don't require emissions tests for free. I used to take mine in and get the readings at idle and 2500 rpm and checked against the graph to see where I was tuning wise.

http://a4.cpimg.com/image/A6/2E/10619814-0cff-02000119-.jpg