The C370 Second Stage is based on SCUBAPRO's compact C350, with a balanced valve added to the design. It uses an exhaust tee derived from the S620Ti to reduce work of breathing, and a compact high-flow mouthpiece, also derived from the S620Ti, for airflow and comfort. It includes a user-adjustable inhalation effort control knob and a small coaxial dive/pre-dive lever. It is sold separately from a first stage and is a compact, lightweight option for divers who want adjustable breathing control.