Diving pressure gauge
The (submersible) pressure gauge, also called SPG, is attached to the 1.stage by a high pressure hose and shows the actual tank pressure, measured in bar or PSI. The best is to choose the unit of measurement you are used to.
The dial should be luminescent or backlighting and the "low on air" section should be highlighted in fluorescent red color, in order to indicate that this is the reserve of air which should be preserved for safety and is not taken into account for the dive planning.
Pressure gauges often come as consoles which allow embedding a depth gauge or a compass as well. Before purchasing a console make sure that it is easy to disassemble for cleaning or replacing items.
To get advice ask the instructors, or share your opinions with other divers in the diving equipment forum.
Look at the diving center directory to find a dive shop or diving center in your region.
All information and opinions provided are general and no substitute for professional advice. Always check with your diving instructor what fits best to your personal needs and to your level of training.