Seems gives the good result first time, but if you don't exit out of the function (add pts sync seems cyclic! )
give other pts don't re-gives the good result?
(no possibility to undo the first 2 points ? )

Click 3 click 4 erase the click 1 click 2 ok !

here click 5 click 6 don't give the same result than click 1 click 2 ! not ok !