Static Apnea Attempt | Freediving Skills

Would be nice to have narration or subtitles explaining the hand signals. I assume tapping on the shoulder is "are you ok?" and the expected response is the "ok" signal. But does the buddy do it when they feel like, or at set intervals? Not obvious to me is the meaning of the "open hand twice" signal, sent by the breath holder. The buddy responds by pushing a button on their watch. My guess is that this mark the point in time when the breath holder felt a diaphgram contraction or the urge to breath.