Which value can be read from the fathometer to indicate depth when powered on?

The fathometer, also known as a depth sounder, is specifically designed to measure the depth of water beneath a vessel. When powered on, it sends out sound waves that travel through the water and reflect off the seabed. The instrument calculates the depth based on the time it takes for the sound waves to return, providing a direct measurement of water depth displayed in various units, such as feet or meters. This capability is crucial for navigation, ensuring that vessels avoid underwater obstacles and navigate safely in shallow waters.

The other options, such as water temperature, water flow rate, and water pressure, are measurements that may be gathered by different instruments and do not represent the primary function of a fathometer. While they are valuable for maritime operations, they do not pertain to the depth measurement that a fathometer is designed to provide.