Thanks ... you've confirmed what I figured out through trial and error. What I also included was a multi dimensional array as part of a CALL routine.
Using the FOR / NEXT function with a IF/ELSE test, I could loop the routine to find the appropriate index value and subsequent temp point.
DM[G] = (ADC(G)-DM[H-1])*(DM[H+100]-DM[H+99])/(DM[H]-DM[H-1]) + DM[H+99]
You need to watch out that for interger mathematics.
101 - 199 - index value = ADC raw value
201 - 299 - temp points for T1
301 - 399 - temp points for T2
etc.
This was easier to program as I used the concatenate function in Excel to generate the definition text string.
e.g. =CONCATENATE(X42,": ",Y42,": ",Z42) which gives
'initialize data table
DM[138]=2310: DM[238]=770: DM[338]=250
DM[139]=2398: DM[239]=806: DM[339]=270
etc.
Then all you need to do is cut and paste ... no extensive typing where you might make a typo.
Hope this helps others.