The idea
A pressure gauge and a depth display answer different questions. The submersible pressure gauge, often called an SPG, indicates cylinder pressure. A depth instrument reports position below the surface. Both can display numbers, so their labels and units matter.
In Australia, you will often encounter metres for depth and bar for cylinder pressure, but equipment can use other units. Before using unfamiliar instruments, ask your instructor to identify the displays and explain the model. A number without its unit is incomplete information.
A useful reading has three parts
Display
Which instrument?
Number
What value?
Unit
What does it measure?
Original YouDive concept graphic based on the lesson explanation and its cited sources. Instructor review pending.
Put it in context
| Idea | What it means | Question to explore |
|---|---|---|
| Cylinder pressure | Gas pressure shown by an SPG | Which unit is displayed? |
| Depth | Distance below the surface | Does the display use metres or feet? |
| Time | A duration or clock reading | Which kind of time is this field showing? |
A QUICK KNOWLEDGE CHECK
Try it for yourself
A self-study check, not a qualification or skills assessment.
Words to know
Sources & further reading
Primary references for the underlying concepts. The learning examples, questions and diagrams are original YouDive material.
PADI: Dive ComputersSources checked 30 September 2026. Lesson awaits qualified instructor review.
This is an introductory self-study lesson. Learn and practise diving skills with a qualified instructor. Mascot art is illustrative, not an equipment-use diagram.