It seems, although The Dash sports “dual pulse oximeter sensors”, it currently is only capable of measuring heart rate with these sensors. Bragi has informed me that, although blood oxygen measurement is possible, it is not a high priority on the roadmap at this time:
From the hardware perspective, it is definitely possible to measure blood oxygen saturation. This was also communicated as a long-term goal when having designed The Dash. However, the operating system has many different conditions that need to be held when wanting to implement this feature. Therefore, Bragi OS still needs to be developed so that measuring further body vitals is possible. I hope it is understandable that our developers were not able to implement those features, yet.