If I remember right, each column can only go up to 60. so add up to seconds, anything over 60 stays and 1 carries over to the minutes. add those up, anything over 60 stays, and 1 carries over to degrees. then add those.
ΑΔΒ = ΒΔΑ because Δ stands for the difference between two numbers and the difference between two numbers doesn't change when switched to the other side.