I just got a scanmaster hooked up to my car. I notice that my O2 sensor readings are all over the place. I've got a 4-wire heated O2 in the car, and I'm not really sure what to expect out of it as far as readings. The readings vary at idle from .085 volts to .8~~ volts. Pretty hard to tune when there is no consistency.
Go to the tech page it will explain the 02 theory
purpose and testing