Lbw appeals happen within the space of two seconds, often less. During that time the umpire has to assess numerous factors before arriving at their final outcome.
The increasing role of technology has brought even greater scrutiny to lbws.
TV viewers can see a decision from numerous angles with the help of computer software which can predict swing and spin.
But the umpire has only one chance to get the decision right.
Graphics by Catharine Green and Kim Lau
The BBC is not responsible for the content of external internet sites