If you program G43 H1, you get an offset from offset #1 in the table, which will affect your tool length by a negative value. If you program G43 H-1, the control doesn't know what to do with that negative number, because -1 isn't a spot in the table. You don't program the H with a direct numerical value. If needed to use the offset value from the table, you'd use it directly, without the G43 or G44, as in: Z[0+#107]. Any clearer?