How do you calculate DOI Dry Operating Index?

[FLEXJET]

You will find in any company's "Ground Operations Manual" the BASIC INDEX AND MAC FORMULA :
see correct formulas on my next post, thanks to john_tullamarine
Index = [W - (Sta - Ref. Sta.) +K] / C
% MAC = [(C x (I - K) + Ref. Sta. – LEMAC] / (MAC / 100)
With :
W = Weight actual.
Sta. = Station horizontal distance in inches or metres from station zero to the location.
Ref. Sta. = Reference station/axis. Selected station around which all index values are calculated.
K = Constant used as a plus value to avoid negative index figures.
C = Constant used as a denominator to convert moment values into index values.
I = Index value corresponding to respective weight
MAC = Length of Mean Aerodynamic Chord in inches or metres.
LEMAC = Horizontal distance in inches or metres from the station zero to location of the Leading Edge of the MAC.