A very important piece of equipment (the bit that keeps you alive underwater!!). Regulators have two basic components (first and second stages)

FIRST STAGE
Unbalanced regulators reduce cylinder pressure to approximately 8 - 10 bar.
Balanced regulators reduce cylinder pressure to approximately 8 - 10 bar but then increase pressure as you get deeper, so retaining the differential between first and second stage, giving an easier breathe at depth.

SECOND STAGE
Reduces the air you breathe to ambient pressure of surrounding water.

A selection of the regulators and octopus rigs available at Slough Scuba Store