I always thought it was calculated differently. The sheaves had numbers 1,2,3 and the helix had numbers 1,3,6,9. So if you put it in 3-3 you get 60*, 3-6 gets you 90*,.6-2 gets you 80 and so on. I always figured it was an addition of the two numbers. The rtx would come stock in the 6-2...