The submersible pressure gauge (SPG - sometimes called the "contents gauge") tells you how much air you have during a Bali scuba dive, in much the same way that an auto's fuel gauge tells you how much fuel you have. You'll learn to use your SPG to plan and control your Bali scuba dive so you return safely to the boat or shore without running out of air. Since you don't want to run out of air underwater, as you might expect, the SPG is mandatory equipment.

A point to remember is that your SPG is a passive device. You have to read it, or it doesn't do you any good. Develop the habit of checking your submersible pressure gauge frequently while Bali scuba diving. With practice you'll get a feel for how fast you use air and won't need to check quite as much, but for now check it all the time. Better too much than too little.

Although SPGs all havethe same purpose, there are a few basic styles and features. These range from gauges that simply tell you your air pressure, to electronic gauges that incorporate other instruments (dive computers). Some of the newest models have no hose, but use a transmitter mounted on the first stage to send air supply data to a computer on your wrist.

Have your PADI Bali Scuba Dive Center, 
Resort or Instructor help you select the best SP(1 when you invest in your regulator. Since it's mandatory equipment, it makes sense to purchase an SP(s along with the regulator.The only preparation required is to have your Bali scuba dive center or resort attach the SPG (or transmitter, if it's the hoseleas type) to your regulator.