Formula problem

[David]

I have a formula problem and i would be greatful if anyone can help. I have 3
cells which i want to multiply together H4,N4,M4. However the cells already
have the following formula in it H4 =1/COS((G4*PI()/180)), M4
=1/COS((L5*PI()/180)) and N4 just has a number in it. There will not always
be a value in M4 and the cell displays #DIV/0! How do i get excel to
calculate H4*N4*M4 regardless of there being a value in M4 but to include M4
if there is a value in it?

 

[Gary''s Student]

=IF(ISERROR(M4),H4*N4,H4*N4*M4)