How do I measure for shot?

From the Laws of the Sport of Bowls (Crystal Mark 4th edition) and Bowls SA's Technical Officials training manual:

When: only once the last bowl of the end has come to rest, or 30 seconds later if a skip asks for the 30-second period (law 23.1). Don't secure a bowl likely to fall during that 30 seconds.

How:

• Measure between the nearest points of the jack and each bowl (law 23.4).
• Use a flexible or string measure when one object is in the ditch and the other on the green (law 23.5). These ditch measures are done by the umpire, not the marker.
• Wedge any bowl likely to fall, and if a bowl rests on another that blocks the measure, secure it before removing the other (law 23.6).
• Kneel with your head over the measuring line. Set the fixed end on the jack, find the nearest point of the bowl, then compare that setting against the other bowls and re-check the first, repeating until satisfied.
• If a marker helps with a long measure, the marker holds the fixed (bullet) end at the jack and you control the measure from the bowls.

Displacement: if your equipment moves a bowl or the jack, laws 37.4 and 38.4 apply.

Point to the shot bowl and confirm both sides agree. Bowls SA's Markers Guide notes that only the players, or the umpire after measuring, may break up the head.