I am assuming the 500 value is the raw value from the LM-2 since your AFR channel is (LM-2 input/68.05)+7.36 = (500/68.05)+7.36 = 14.69933. If that is true, then the 500 value is probably an ADC value representing a voltage the LM-2 is seeing. Then lambda should be (LM-2 input/1024)+.5 = (500/1024)+.5 = .988281 lambda. Do the open air test mentioned above and see if the lambda value on the LM-2 matches what is showing up in the scanner (with the lambda math noted in this post).