Alternate Air Source
The Alternate Air Source is often called the Octopus and is your backup second stage regulator. It works just the same as the primary second stage regulator and can be used in the unlikely event that your primary fails or your dive buddy needs to share air. It is usually a bright color such as fluorescent yellow or pink and is normally secured somewhere within the triangle between the chin and the bottom of the rib cages, normally on the right side.
BCD – Buoyancy Control Device
A Buoyancy Control Device or BCD for short (also known as a Buoyancy Compensator or BC) is the jacket that scuba divers wear.
In colder water it is normal to wear neoprene boots with open heeled fins to keep the feet warm. These boots are normally called booties. They are also used to protect the feet, particularly when shore diving, and some divers find them more comfortable than full foot fins.
An underwater compass is a very handy navigational tool and is a common piece of equipment for divers to carry. Compasses can be attached to gauge consoles, worn separately on the wrist, attached to the band of a watch or dive computer, and digital compasses are now even built into the latest dive computers.
The dive cylinder is also commonly called a tank and is what you use to carry your compressed breathing gas (usually air). Dive cylinders are typically made out of aluminum or steel and come in various sizes with the most common size being 90 cubic feet / 12 liters. Breathing gas is compressed inside the cylinder at up to 3000psi/210bar.
This gauge shows you how deep you are. Depth is measured in either feet or meters.
The most basic dive computers will tell you your depth and dive time but it is also common for dive computers to calculate no-decompression limits over multiple dives. Many newer dive computers will also track air consumption and temperature and some even have built-in electronic compasses. Dive computers are commonly found attached to gauge consoles or worn on the wrist like a watch and can now be found built into masks.
It is good practice to carry a dive knife or shears. Dive knives are not used as weapons, they’re used to free yourself from entanglement, particularly from fishing line. Many divers carry more than one knife for added safety and it’s advisable to wear one on the BCD and one strapped to a leg.
Fins are commonly called flippers by non-divers. They are long flat rubber or plastic extensions of your feet that allow you to swim with much greater ease and speed. The two primary varieties of fins are full-foot and open-heeled. Full-foot fins completely cover the foot like a shoe and are most commonly used in warm tropical water. Open-heeled fins have a strap across the back and are worn with booties to allow the feet more warmth and comfort.
This is what you use to breathe the air from the cylinder.
At its most basic a snorkel is a plastic tube that allows you to breathe while you’re swimming on the surface. It is normally attached to the left side of the mask. It’s a great way to conserve the air in your cylinder while swimming on the surface. Snorkels also come with such features as purge valves (to make it easier to clear any water inside) and splash guards (to make it hard for water to splash in the top).
Submersible Pressure Gauge
The Submersible Pressure Gauge (more commonly called SPG) is the gauge that tells you how much air you have left in your tank. Air pressure is measured in PSI or bar. Most SPGs have a section of the dial highlighted in red which shows you when you’re getting low on air.
Most people need weights to sink in water. There are two common weight systems: The Weight Belt and Integrated Weights.
Wetsuits keep you warm while underwater. They are made from neoprene and designed to be worn snugly in order to allow little water to move against the diver’s skin. They work by insulating the diver from the cold water. Wetsuits come in many sizes from one millimeter to seven millimeters or more, with the most common sizes being 3mm, 5mm, and 7mm.