The rule is that if 50% or more of the ball is hitting 50% or more of the stump then it’s officially hitting, so if Umpire’s Call was Not Out, then the call is reversed. If less than 50% of the ball is hitting less than 50% of the stump then an Umpire’s Call of Not Out stands. If, on the other hand, the Umpire calls Out, then even if less than 50% is hitting, the batsman is still out.
So it all depends on what the Umpire’s original decision is. To some extent all technology has an error margin, as indeed all humans do!
Thank you for the explanation.
So in essence it can work for or against the batsman/bowler, depending on the original decision.