The system has been calibrated and tested, the software will draw the same line today, tomorrow, a week next tuesday until the software gets changed.
Hawkeye do not draw the yellow lines, the TV companies do all the graphics we see on screen, BT use a tool called Piero. They use very very fines lines in their system, the TV companies then slap their graphics over the top. It is all explained in this below. This feature also explains 4pools issue and why he is wrong with his claims about dodgy lines, it is all down to camera angle and perspective.
https://www.radiotimes.com/news/2015-02-10/why-can-nobody-in-football-draw-a-straight-offside-line/
Anyone who has ever been to a horse race or dog race maybe has wandered over to see an actual photo finish picture posted. There, at least at the track I went to, they also have three pictures of a photo finish as reference. One view point from down past the photo finish line. One from on the photo finish line. And the third view point from up past the photo finish line.
All this to show angles of perspective.
I've post this before in here. And is nothing new to me at least.
When one does the railroad rails view, where you are in the middle and see the two rails converge further ahead, this shows how lines are not parallel to infinity ahead of you.
However, you can move 50 feet, 100 yard, or a 1/2 mile up the track and where you stand you still have parallel rails.
And this is my point about picking out two lines which should be parallel. With infinity ahead and behind, the lines do converge. But when you pick out 20 yards or so worth ( the bit on the pitch in the picture with the lines) those two lines should be parallel.
What you don't see is the line drawn on the pitch from sideline to sideline from the last defender. That, for me, would prove the line is straight and parallel to the end line and half way line.
And from that Radio Times article...That doesn’t mean mistakes still can’t happen, as Fifa in the past have admitted.