What is the required size of the black disk at the bottom of the pool?

The required size of the black disk at the bottom of the pool is 15 cm in diameter. This size is typically used in aquatic settings for visibility purposes, particularly in determining the depth of the water and helping swimmers gauge their distance from the bottom. A disk of this size provides sufficient contrast against the pool bottom, making it easier for lifeguards and staff to monitor underwater conditions and assist swimmers if needed.

While the other sizes may be used in different contexts or settings, 15 cm has been standardized in many aquatic facilities to ensure uniform safety and awareness in the water. This standardization allows for consistent monitoring and assistance across various pools and helps in training staff to recognize important visual cues that contribute to overall safety in aquatic environments.