What principle states that all valves should be within reach of the diver?

The principle that all valves should be within reach of the diver is known as accessibility. This principle emphasizes the importance of ensuring that critical equipment and systems, such as gas valves, are easily accessible to divers while they are in the underwater environment. This is crucial for safety and efficiency, as it allows divers to quickly manage situations that may arise, such as gas supply changes or emergencies that require immediate valve adjustments.

When valves are positioned with accessibility in mind, divers can operate them without unnecessary effort or risk, even in potentially hazardous underwater conditions. Achieving accessibility enhances the diver's ability to respond swiftly to changes in their environment or equipment status, thereby contributing to overall dive safety and effectiveness.

The other principles such as visibility, efficiency, and durability are also important in dive planning and equipment use, but they do not specifically address the ease of access to valves in critical situations like accessibility does.