Which of the following is NOT typically required by umpires during competitions?

The choice that is not typically required by umpires during competitions is the use of visual aids only. Umpires are responsible for making precise measurements and ensuring the fairness of play, which necessitates the use of specific measuring tools.

Callipers, flexible measures, and string measures are all essential equipment that assist umpires in accurately assessing distances related to the bowls. Callipers are used for measuring the distance between the nearest bowl and the jack, providing a precise measurement. Flexible measures, which are often used to determine close distances, can conform to various shapes and angles, making them practical for measuring on the greens. String measures also allow for accurate distance calculations and are used frequently to clarify the positioning of bowls in relation to each other and to the jack.

In contrast, relying solely on visual aids does not provide the precise measurements needed for competitive play. While visual aids may help umpires in assessing situations, they do not suffice as a standalone tool for the critical tasks required in officiating bowls competitions.