There are many kinds of gauges. There are three main types: Analog, Digital and Pneumofathometer models. You need to find the right gauge for your diving needs. Your gauge must be calibrated at all times, especially when diving at high altitudes.
Analog gauges
Analog gauges used for gauge diving are useful in helping divers determine the depth of water. You can use them to indicate the depth by turning a needle around a graduated scale. These gauges can be worn around the wrist or integrated into a dive computer. The analog ones may be more reliable than digital gauges, but they are not completely accurate. An analog gauge has one advantage: you won't run out of batteries.
The gauge's display is easy to read. The gauge has numerical increments that range from 10' to 40’ and 20' up to 150'. It also has a pressure gauge. It displays pressure between 0 and 5000 psi. The screen displays reserve air and the green screen main air.
Digital models
Many divers want to stay long and dive deep, but a digital gauge won't help them do this. The difference in pressure between the gauge and the ambient water can be affected by temperature changes. Fortunately, a mechanical gauge is much safer than an electronic gadget. The gauge can keep track of your dive time, depth and will also calculate your Nitrogen retention to prevent you from getting decompression sickness.
There are two types of digital gauge dive computers. The hose approach is simple and uses a pipe to connect the diver's computer to the high pressure port at the top of the first stage. Wireless mode uses an electronic transmitter to communicate with the computer. This type can be used with console and wrist-mounted models.
Pneumofathometers
Pneumofathometers allow you to determine the depth of oxygen supplied to your diver. These devices measure air pressure at the surface and then indicate the depth in feet or metres. These devices were once mounted on a hand crank air pump, which supplied breathing air to the standard dive suit. The air supply was free flowing, with no back pressure.
Gauge diving is for divers who wish to use a gauge. A gauge should be able to read between 130 and 160 percent the maximum operating pressure of the diving system. For systems that operate at 3,000psi or higher, a gauge with this range will suffice.
Submersible pressure gauges
A submersiblepressure gauge (SPG), allows divers to keep track and monitor their air pressure. It also displays the current depth and the direction the diver is moving. An SPG is typically attached to the regulator by a high-pressure line. This arrangement is useful for divers to avoid getting confused about the location of the gauge and helps prevent it from being lost. An SPG displays the air pressure remaining in pounds per square inch. This is useful for monitoring air supply when diving.
Scubapro manufactures an oil-filled, analog depth gauge. The Bourdon tube design measures down to 200 feet. For greater versatility, it also includes a C1-compass that attaches to its console boot. This gauge is best suited for beginners because it is simple and easy to use.
Compass
The easiest compass for gauge diving to use is one that is easy enough to read. The compass should be large enough to be read underwater and be marked with the appropriate markings. Look for a compass with a bezel with compass headings grouped in 30-degree increments and indicator marks every five degrees.
A side view window is an important feature of a compass that allows gauge diving. It lets the diver see the direction in which the compass point. This allows the diver's to see the direction the compass is pointing even when it is dark.