Thanks for eveyone's help. I wound up using the following formula:
=IF(K3>=L3,"nm",IF(K3<$B$1,"nm",IF(K3>I$1,"nm",IF(L3<$B$1,"nm",IF(L3>I$1,"nm",((HLOOKUP(L3,$B$1:$I$199,ROW(),FALSE)/HLOOKUP(K3,$B$1:$I$100,ROW(),FALSE))^(1/(L3-K3))-1))))))...