Which of the following features is critical for tracking ascent rates in diving?

An ascent rate indicator is critical for tracking ascent rates in diving because it specifically measures the speed at which a diver ascends towards the surface. Maintaining a controlled ascent rate is essential for avoiding decompression sickness, commonly known as "the bends." This device provides real-time feedback, allowing divers to adjust their ascent speed if necessary, thereby ensuring safe ascent profiles during a dive.

Depth gauges are important for knowing how deep a diver is and can indirectly indicate how far a diver still has to ascend, but they do not specifically track ascent rates. Time-to-surface calculators provide estimates about when a diver will reach the surface based on current depth and ascent rate, but they are not as effective in providing immediate feedback on ascent velocity. Gas consumption monitors track how much air a diver has remaining but do not contribute to tracking the speed of ascent. Therefore, the ascent rate indicator is the most direct and essential tool for monitoring ascent rates in a safe diving practice.