I talked to some math gurus where I work and here's what they came up with for calculating the relationship between knob marks and the actual wire feed speed for the Miller 211 MVP machine. I'm not a math guru so I can't proof their work but playing with various values of X the results for Y sure look like the fit the bill.
This formula is based on the relationship between the dial indicator marks of 10 to 100 and the real specs of the machine as posted by Miller of 60 to 460 IPM.
Using Y as the unknown and X as a value between 10 & 100:
The forumla is: y=(40/9)x+(60-(400/9))
That also works out to: y=(4.444444444*x)+15.55555556
Simpler (but less accurate) to round off to: y=(4.5*x)+15.5
Couple of rounded examples are if the dial is set to:
25 then IPM is 127
70 then IPM is 326
99 then IPM is 455
If you want to plot a graph in Excel:
Put the known data points into two rows (Row A 10 & 100, Row B 60 & 460)
Select the 2x2 grid you just created
Then choose Insert -> Select: Scatter (With Straight Lines)
This will draw a line you can trace intersecting lines on from the two axes and find the actual IPM.