The idea is to catch the Pidgey when you start the game, save, and turn off the DS. Then, plug in the AR, launch the game, and look at the IVs.
The game determined the delay of the Pidgey when you caught it based on the IVs. If you plug an AR into the DS, and launch the game, the delay for that Pidgey will still be the same because the IVs never changed.
As for calibrating with the AR, well, I have never RNG'd a Poke with the AR. Let's just say that not only have never hit my delay, the Elm responses I receive don't show up in RNGReporter, even with -99/+99 either way. So I actually have caught all those legends on my own with hard work, I couldn't use a 100% catch rate code because I didn't use the AR to RNG them.
It's not bad, really, quite simple once you get the hang of it. :)