On some
mods you can choose between RMS or AVG.
in the most basic of terms the RMS takes the setting you ask for and adjusts the chip to match that setting. by doing the RMS calculations in the link above.
in AVG or average, the
mod will fire from 0 to 6v really fast and average out the reading to give you something close to your setting, it used to be the way a lot of mods worked but it is very unreliable and can burn your wicks, you could set the
mod for 4 volts and it could give you 3.6V or maybe this time 4.5V and usually everything in between everytime you hit the button.
there is more to it then that but that is the simplest way to explain it.