If negative, enter zero(0)

The program uses a zero rather than a dash in the program, but it has the same result. 

The income base cannot be less than zero. 

"19. Ohio income tax base (Ohio IT 1040, line 3 minus Ohio IT 1040, line 4). Place a “-” in the box

at the right if the amount is less than zero"

https://www.tax.ohio.gov/portals/0/forms/ohio_individual/individual/2018/SDIT_SD100_Bundle_FI.pdf