When a freediver is diving shallow, a computer is not such an important requirement. For snorkelers diving the 10m range, the use is more for interest. However as the freediver gets deeper the importance increases.
In recreational freediving, as in spearfishing or photography, the computer becomes a great diving aid. It is good to know one’s depth and duration during a dive but this is not the main role of the computer. For safety reasons recreational divers shouldn’t be monitoring their computers to tell them when to surface. The diver should be using his innate and tuned perceptions of his body’s condition during an underwater breath hold. The main use of a computer in this level of diving is to monitor the freediver’s recovery time on the surface. The computer tells him the depth and duration of his last dive and ticks off the time of his recovery. It is easy to dive before one is fully recovered, causing the diver to tire quicker during the day. Whereas a good recovery between dives will find a diver able to reach his full potential for a much longer period. Some recreational freedivers set the dive computer alarms to alert them when they reach a certain depth. In very clear water it can easily drop deeper than intended. This is not often done by spearfishers as the alarms can frighten wary fish.
There are some recreational freedivers diving deep enough to become a risk for Decompression Sickness. The monitoring of surface time compared to dive time becomes vital, as is a full understanding of the risks, precautions and emergency procedure.
In competition freediving a dive computer is a vital part of a diver’s kit. In competitions, a freediver dives with two computers. His own and the competition computer. Each freediver is given a competition computer to officially measure the depth of the dive. It is usually worn on the wrist of the hand that will reach for the tag on the base plate. This will give the deepest reading. The competition dive computer is important for a situation where the diver turns early and doesn’t reach the target depth but the depth of his dive is needed. Penalties are given for the distance the freediver is short of the target.
A freediver usually has his/her own dive computer configured to give reminder alarms at different stages of the dive. These are usually but not always, an alarm to remind the diver to takethe mouthful, needed for equalization at depth, and an alarm to warn the freediver he is approaching the targeted depth. It is easy to become so relaxed in a dive that without this second alarm, divers have hit their heads on the base plate.
This varies from person to person depending what requirements the freediver have. Scuba divers want a watch with all the scuba capabilities as well as the freedive mode. Some divers prefer a large display, where others want the computer to be less intrusive, perhaps to wear all the time. Most of the computers do the functions freedivers require, with small differences.