# Observe the water level until it drops to the 15 cm depth, at precisely 15 cm, commence timing, when the water level reaches the 12.5 cm depth, stop timing, record the time in minutes. | # Observe the water level until it drops to the 15 cm depth, at precisely 15 cm, commence timing, when the water level reaches the 12.5 cm depth, stop timing, record the time in minutes. |