Hi lueker,
I would use VLOOKUP to refer to those Values in the data sheet.
I know this is not the same as your calculation, one reason being you
stated you would only be using the second of the two values (Equivalent
length of straight pipe). Also, I know precious little about hydronic
piping. Anyhow, say the calculation is Pressure drop = K-value *
Equivalent length of straight pipe. Also, say you data on the data
sheet occupies range A1:C50, with "Fitting" in Column A, "K-Value" in
Column B and "Equivalent length" in Column C. Also, say on the calc
sheet (Assuming "calc" is the sheet name) cell A1 is the destination
cell for the fitting value (eg 1" 90° Elbow), either by keyboard
input, copy/paste or validation list, and that the formula is in B1.
Then, using my silly formula as example, the formula in B1 would be
=VLOOKUP(Calc!A1,Data!A2:C50,2,FALSE)*VLOOKUP(Calc !A1,Data!A2:C50,3,FALSE)

Ken Johnson