finishing lines

skirting, when we did our finishing lines we would measure up then go cut a 45 degree angle out of one end, then cut most the way up that 45 degree angle with a 90 degree angle then we would get a hack saw and cut all the way up the cut until we we mm from the edge of the cut, this would leave us with a small triangle at the top, this allows movement in the house and stops cracking in paint work. it almost looks like two 45degree angles meeting.