Hi

Rather than changing the display format you can change the o/p
itself...

this can be done by using following formula

=if( yourformula=0,"-",yourformula)

this means when the answer is 0 it will return dash otherwise the
result.

added to this you can also keep the formatting
#,##0.00;[Red](#,##0.00) so that negative values would be shown as red

Regards
NC