The current formula...

=($C$10/2)/COS($C$11*(PI()/180))*$C$16*VLOOKUP('Data Tables'!A13,'Data Tables'!A15:I22,7)

I have tried;

IF(ISNA(($C$10/2)/COS($C$11*(PI()/180))*$C$16*VLOOKUP('Data Tables'!A13,'Data Tables'!A15:I22,7)),"-",($C$10/2)/COS($C$11*(PI()/180))*$C$16*VLOOKUP('Data Tables'!A13,'Data Tables'!A15:I22,7))

But for some reason can't get it to work...

Any suggestions?

Thanks