You can do it crudely by working out the gradient between each %load and then interpolating between them by having set ranges and domains between 0%, 25%, 50%, 75%, and 100%. Another way you could do it is to plot the graph of these points, and then draw a curve/line of best fit, which you could use to estimate graphically any load/burn rate combination.
If it works out to be a fairly linear graph, you could use linear regression to calculate a line graph equation, which can be used as a "plug and play" formula for your results on burn/load.
If you need any more information on any of these suggestions, just shout.
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