Pretty much the most important function of a diving computer is the ability for it to monitor all factors on a dive that will keep its user safe, and one of the most important of those is the build-up of nitrogen and helium due to pressure at depth. In other words, the decompression model.

A very common way for new divers to ensure that they are diving safely are dive tables. They allow a diver to first select a depth and will then show a maximum allowed dive time. When performing multiple dives the depth can be combined with a time to track nitrogen/helium intake over the dive and inform any restrictions that may impose on future dives. Tables are, by there very nature, very conservative, in most cases only allowing the diver to plan for a single depth. They will use what is referred to as a square profile, where the diver descends immediately to their maximum depth and stays there until ascending to their first stop. A computer can often allow for the diver to stay longer underwater as it will track their depth as it changes, rather than assume they are always at the maximum. When a diver is shallower they will be taking on less nitrogen/helium, and in some cases may even be lowering the saturation in their tissues, known as off-gassing.

When looking at how decompression obligations can be tracked, there are two main (open source) algorithms that dive computers use. The first and I believe most common is the Baulmann gradient factor algorithm which breaks the body down into a series of compartments and tracks tissue pressures in each one. The second is the variable permeability model (VPM), specifically VPM-B, which tracks the growth and pressure of a bubble in each compartment.

Due to my own experiences, I will first be implementing the Baulmann model and will cover both the details of the model and how I have implemented it in a later post.