I have the formula of

=IF(ISBLANK(D18),"",IF(E18="unknown","",(IF(ISBLAN K(C18),(F18),(PRODUCT(C18,F18))))))

and I am getting an inconsistant formula error message.

C18 is the quantity code
D18 is where an item catalogue code would go
E18 is where the item description would be displayed (as is set to display
unknown if the code is unrecognised)
F18 is the unit price

Can anyone give me a direction as to why the formula seems to be working
correctly, but is returning an error of an inconsistant formula.

thanks