Linear interpolation of large data sets

Originally Posted by Avren

Sure thing. The relationship looks like this:

First, you take the difference between the desired value and the lower value of the data the desired value resides between, and divide it by the difference between the higher value and the lower value that describe the region the desired value lies within, ie:

(211-210.778)/(212.268-210.778)

This gives the point along the line between the higher and lower values that the value you want lies at as a percentage. You then apply that percentage to the linear relationship of the related data for n and k. A reasonable explanation is found on the wikipedia page for interpolation. This is Linear interpolation.

Are you then not assuming a linear relationship between nm, n and k? That was the reason for me asking the above question; it might not be linear. In any case, if it is linear, then, assuming your data starts in A1, in D1:

=B1+(B2-B1)*(ROUND($A1,0)-$A1)/($A2-$A1)

Copy down and to the right. Does it work?