When should I call the umpire?

Under law 42.2.15 of the Laws of the Sport of Bowls, if either player is not satisfied with your measure, you must ask the umpire to measure. If no umpire has been appointed, choose a competent neutral person to act as umpire; their decision is final.

Bowls SA's Markers Guide for Beginners also says to call the umpire:

• if, after centring, you doubt the jack is at least 23 m from the mat line (after consulting the players), and always if either player asks;
• if the jack is moved in play to what you think is less than 20 m from the mat line, before the next bowl is delivered (always if either player asks);
• if a player delivers the opponent's bowl and you are unsure of replacing it without disturbing the head;
• whenever you have any doubt, can't make a decision, or face a close or difficult measure;
• for measures with the jack or a bowl in the ditch, which are done by the umpire;
• to report any infringement of the laws you notice, and any irregular markings on the bowls.