I denote delay timing as "@ value". As you can see the picture above, C_in0(carry in 0), A0(input A's 0th bit), and B0 are initially ready so there is no delay which means they all have @0 delay. The rest of delays is also indicated on the picture.
My Question is why S0 is @2 not @1.
To my knowledge, the sum part in Full Adder has 2 levels that are xor both. Therefore if an incoming Cin's delay is n, the total delay of the part is n+1. For example, if you look at FA2 in the above picture you can see Cin1 is @2 so S1's delay is 3(2+1).In my example, Cin0 = 0 so the S0's delay should be 1. Maybe the picture below helps you understand what I am saying.
