DIV/O Error
 

Here is the wrong way:
=IF(B91/(D4*D87+E4*E87+F4*F87+G4*G87+H4*H87+I4*I87),(B91-(D4*D87+E4*E87+F4*F87+G4*G87+H4*H87+I4*I87))*0.5+( D4*D87+E4*E87+F4*F87+G4*G87+H4*H87+I4*I87)*0.16672 2)

This example was kindly provided and I must post for those at my level to
learn the better practice approach.

=IF(SUMPRODUCT(D4:I4, D87:I87)=0, "", IF(B91<0, B91/2 -
SUMPRODUCT(D4:I4, D87:I87) * (0.5 - 0.166722),""))


Thanks jem!