Ok lets ignore most of the other stuff in a FI system and the million and one things that determine engine performance/efficiency.

In very simple terms, you have fuel and air going in, a bang, and gases going out.

The bikes ECU will have a stock fuelling BASE map that is fixed and determines how much fuel gets squirted in (multiplied by correcting factors, depending on information from the various sensors, and too many variables to mention here).

The O2 sensor in the exhaust, this gives feedback to the ECU to allow for some on the fly adjustment of the fuel going in eg for a given set of constant conditions the ECU gives X amount of fuel, but the O2 sez you need more/less than X depending on the real time O2 reading?

So in a stock XTZ while the bike is running, the FI system will constantly be tuning itself within some small tolerance to an optimum O2 reading?

When on the dyno what to you tuners use as the base for tweaking the fueling is it the AF ratio?