Which device is primarily used for measuring the depth of water?

The depth sounder is the correct choice for measuring the depth of water, as it is specifically designed for this purpose. It uses sonar technology to send sound waves down to the ocean floor and measures the time it takes for the echoes to return. By calculating this time, the depth sounder can provide an accurate reading of how deep the water is at a particular location.

In contrast, an anemometer is primarily used to measure wind speed and direction, which is unrelated to depth measurement. A chronometer, which is a precise timekeeping device, is essential for navigation purposes, but it does not offer information about water depth. A compass is used for navigation and orientation, indicating cardinal directions, but does not measure water depth at all. This clarification highlights the specialized function of the depth sounder in marine operations.