SPG — Submersible Pressure Gauge

The SPG or submersible pressure gauge is the device that tells you how much air remains in your cylinder. You typically find it attached to your primary regulator console via a low-pressure hose. Most modern gauges show readings in bar or PSI, which helps you track consumption as you descend.

I once saw a student panic because they misread a 50 bar reading for 150 bar. Always check your gauge every few minutes during the dive. You should begin your ascent when you hit your pre-planned reserve limit, which is often 50 bar in many recreational settings. A reliable SPG prevents unexpected out-of-air emergencies. Check your hoses for cracks before every trip to places like Koh Tao.