I would think that you merely need to know what the actual amperage/voltage is vs the dial indicated. ie; dial says 400 amps / 28 volts but actual is 408 amps / 27.5 volts...that way you can make adjustments to be sure that you are welding within your procedure.

I have a form that is in 50 amp increments around the intended range and then just fill in the actual vs the dial indicated....this gives the welder something to go on.
my .02 worth