What are the rules on measuring and deciding the shots?

Under laws 22 and 23:

• Shot bowls are the bowls nearer to the jack than the nearest bowl of the opposing team or opponent in Singles. No bowl may be moved until the opponents agree whether it is a shot, except where a bowl must be moved so another can be measured.
• Deciding the shots must not start until the last bowl of the end has come to rest, or 30 seconds after that if either skip (or opponent in Singles) asks for the 30 seconds, for example to see whether a bowl lying at an angle will fall. No bowl likely to fall may be secured during that period.
• Measuring before the process starts is not allowed. If a player does, the defaulting team or opponent loses the right to play any bowls remaining in that end and the other side delivers its remaining bowls.
• All measurements are made between the nearest points of the jack and the bowl. Between a jack in the ditch and a bowl on the green (or the reverse), a flexible or string measure is used wherever possible.
• If a bowl is likely to fall, either opponent can secure it by the best available means. If a bowl falls of its own accord during the process, it stays in its new position and the shots already agreed still count.
• Shot bowls can be placed in a group away from measuring, and the number in the group must be agreed by the opponents.
• The third can measure any and all disputed shots (law 40.2.1).

Source: World Bowls, Laws of the Sport of Bowls Crystal Mark Fourth Edition, laws 22, 23 and 40, https://www.worldbowls.com/wp-content/uploads/2023/05/Laws_of_the_Sport_Fourth_Edition.pdf