You can't use those meters for car tuneing. They're dodgy firstly and secondly they are only good for ratios right around 14.7:1(stoichiometric ratio).
You need to use a wide band sensor that dyno tuners use, quite expensive, they also have heaters in them to heat the sensor up so it operates correctly.
At the back of the car, when you screw it onto the tailpipe they don't get hot enough and you must have its own internal heaters on to get accuracy.
Would be great if we all threw in $100 each and used it for the club.