What does a dive depth gauge monitor?

A dive depth gauge is specifically designed to monitor the current depth of the diver. This instrument provides real-time information about how deep the diver is submerged, which is crucial for both safety and navigation. By knowing the depth, divers can avoid exceeding their limits, prevent decompression sickness, and adhere to the proper ascent rates. Monitoring the current depth also allows divers to manage their air consumption more effectively and ensures they stay within the safe operational parameters while underwater.

The other options relate to different aspects of the diving environment or diver condition but are not functions of a depth gauge. For instance, visibility underwater, water temperature, and heart rate can be monitored using different instruments or devices, but they do not pertain to the primary function of a dive depth gauge. Therefore, the depth gauge's main purpose remains focused solely on measuring the diver’s current depth.