[ByronRACE]

A MAF can be calibrated.

A MAF can be flowed with or without being calibrated and a resulting curve plotted/charted.

And, the PCM can be calibrated with any massflow vs voltage function, or left stock.

This whole business of "calibrated mafs" started when someone realized they could divide down the maf voltage output of a maf in order to stick a 24lb injector on a 19lb/hr mustang and make it still run without messing with the PCM. Basically, they lie to the PCM about how much air mass is entering the engine, and this lie causes the PCM to reduce injector pulsewidth just enough to make the wrong injector run correctly. You can do this trick up to about 30lb/hr injectors without too many side effects. Bigger than that, and other side effects begin to occur (minimum maf voltage below .4V at idle flags a code, etc).

The right way to do things (the OEM way) is to size a mass-air transfer curve with a measurement range that best fits the engine so you use the entire voltage range of the output, then program the PCM with the appropriate curve. This way you end up with the best possible resolution.

For example, if you were to take a MAF that is capable of measuring 4500kg/hr of airflow and put it on an engine that only flows 1000kg/hr at max rpm wot, you are only using less than 1/4 of the available 0-4.8V range and your resolution is 1/4 of what it should be, and resolution suffers.

Assuming the maf is appropriately sized, measures the proper range, and has been flow mapped...the way to calibrate the PCM is to put that curve in there with the actual injector size and true engine displacement and work forward from there. This is true for anything up to about 90lb/hr. Beyond that, you have to start playing games to make the ol EEC-IV work.