The ONLY way to qualify them is to be able to verify the O2 switching at a rate of ONCE per second, NOT 10x per second like MANY people think it is. To be able to verify the O2, you need a visual. People would say, " I can use a DMM or DVOM (digital multimeter or digital volt/ohm meter)... But i would say, NO. Because you can NOT see when it switches and HOW fast it switches, therefore, the only way to verify the O2 is thru viewing of an oscilloscope or some sort where you can visually see and calculate the switch rate from Rich to lean or Lean to rich within 100ms.

Hopefully this clarifies things for yah.