I am using Index & Match function to find values in the set of array (table). If the lookup value for both the match functions exist in the table/array then display the corresponding value otherwise interpolate between the highest(Match,-1) and lowest values (Match,1) from the lookup value for both the match functions and display.

Here is what i used:

=INDEX(C10:AE259,IF(MATCH(F3,B10:B259,0),MATCH(F3,B10:B259,0),((MATCH(F3,B10:B259,-1)-(MATCH(F3,B10:B259,1)))/20)*MATCH(F3,B10:B259,1)),IF(MATCH(F2,C8:AE8,0),MATCH(F2,C8:AE8,0),((MATCH(F2,C8:AE8,-1)-(MATCH(F2,C8:AE8,1)))/10)*MATCH(F2,C8:AE8,1)))

It only shows the values which exist in the table/array but the formulae for interpolation that i have put doesn't work. how do I make the it work? I know that I have done something wrong with the use of IF formulae but I don't know how else to do it? Please help!