I am trying to calculate the average propagation time carry_TP from carry_TPHL and carry_TPLH which I already got the expression from the calculator tool and works well. Now how do I make the third output expression for carry_TP = (carry_TPHL+carrt_TPLH)/2? What I have tried (shown in image) isn't working for me. I am using the cadence icfb V5.