How do dive computers assist with dive planning?

Dive computers play a vital role in dive planning by monitoring various factors that influence diver safety and efficiency underwater. Option C identifies how dive computers can enhance bottom time. By crediting time spent at shallower depths, dive computers allow divers to maximize their allowable dive times at deeper sections, thus providing a more efficient use of the dive profile. This feature is essential as it helps divers to stay within safe limits and manage nitrogen absorption effectively, ensuring a reduced risk of decompression sickness.

In contrast, while providing underwater navigation and determining dive routes are important, these functions are not the primary focus of dive computers. Similarly, while calculating necessary gas supplies is an important aspect of dive planning, it typically relies on predetermined formulas and inputs rather than being an automatic function of a dive computer. Overall, the ability of dive computers to assist in calculating bottom time through depth crediting makes them invaluable tools for divers managing their dive physiology and safety.