Hello Gill,
Could you please provide an example where ABS would get fail in your situation?
Also the solution I provided has handled the 0 just modifying it for the sake of null values below.
=If [LY]<0 Then Abs([TY]/[LY]) Else If ([LY]=0 Or IsNull([LY])) Then 0 Else ([TY]/[LY])
Regards
Niraj