Maybe this will give some ideas on how it might be done:
Cells C2-4, G2-4, K2, K4, M2, M4, B7 and B8 are referenced using "Defined Names". The names they have been given are in the cells immediately to the left of them. I.e. C2 is named P. You name a cell in Excel 2010 by selecting the cell and typing the require name in the name box, which is immediately tot he left of the cell formula editing box, in my example it currently says "F11". See here for more help :
Define and use names in formulas - Excel - Office.com
B7, B8 and B10 contain formulas, which are copied as text into the adjacent cells in column D.
The diagram tries to illustrate how the Defined Names relate to the problem.
What I have done is assume that at a given weight (W), the divider value is a direct linear relationship with the position value (P) as it changes from its lowest value (
Pr) to its highest (Pf). So if W is the lowest possible weight (Wl), as P changes from
Pr to Pf, the value of divider will linearly progress from Bl value to Br. As W is increased the range is altered linearly. These are the Sl and Sh values: where Sl linearly changes from Bl to Tl as W increases from Wl to Wh, and similarly for Sh.
Divider is then calculate as a linear proportion of the range Sl to Sh as P increase.
The Orange cells need to be populated with the divider values at the extremes of your weights and positions.
The green cells need to be populated with the extremes of weights and position.
The blue cells then become your inputs for actual weight and position.
Samples:
P = -2 i.e.
Pr fully rearward.
W = 250 i.e. Wl the lowest weight.
Divider is given as : 3000
P = 2 i.e.
Pr fully forward.
W = 250 i.e. Wl the lowest weight.
Divider is given as : 3300
P = -2 i.e.
Pr fully rearward.
W = 450 i.e. Wl the highest weight.
Divider is given as : 3300
P = 2 i.e.
Pr fully rearward.
W = 450 i.e. Wl the lowest weight.
Divider is given as : 4500
There is an intermediate sample in the capture shown above.