Complex sentence: The first stage typically has at least one outlet port delivering breathing gas at full tank pressure which is connected to the diver's submersible pressure gauge or dive computer, to show how much breathing gas remains in the cylinder.
Split into simpler sentences: The first stage typically has at least one outlet port delivering breathing gas at unreduced tank pressure. This is connected to the diver's submersible pressure gauge or dive computer, to show how much breathing gas remains in the cylinder.