How does an electronic review (challenge) work?

At tournaments using an Electronic Review System (2026 ITF Rules of Tennis, Appendix VII):

1. A player can ask for a review of a line call or overrule only on a point-ending shot, or by stopping play during a rally (a return is allowed, but then the player must stop immediately).
2. The chair umpire should use the review when there is doubt about the call, but may refuse an unreasonable or late request.
3. In doubles, the appeal must stop play or be made so the chair umpire stops play. If the procedure was wrong or late, the chair umpire may decide the opponents were deliberately hindered, and the appealing team loses the point.
4. If the system can't make a decision, the original call or overrule stands.
5. The review result is the chair umpire's final decision and can't be appealed.

Number of challenges: three unsuccessful appeals per set, plus one extra in a tie-break. In advantage sets, players get three again at 6-6 and every 12 games after. A match tie-break counts as a new set (three appeals). Successful appeals are unlimited.