Monitoring O2 sensor/voltage

[bruce plecan]

I'd appreciate a little clarification, on this GM O2 sensor monitoring.
If all they did was measure the output from the sensor, then I could
understand that it was just reading the voltage.  But, by appling a
voltage to it, and it having to develope enough current, and voltage
to alter that signal doesn't that change what the ecm is monitoring
from straight voltage, to wattage?..
TIA  Bruce    Further documentation of why I own several cone
                     shaped hats...