Logically all three of these should produce the same results as the formula is "Output = Side - Input" results in 13 - 15 = -2.

However, the first one in the row acts as of it's first Comparator is an inverter more like the second screen shot (which logically is 15 - 13 = 2).

Can we get clarification as to this behavior. As this is causing a lot of folks confusing including myself.