Measuring Blood Saturation. Would that be possibile?

Sorry for the probably naive question.
Might it be possible to measure blood saturation, possibly estimating it using an algorithm?

Yes. There is a thread open about what we can get from the PPG sensor (heart rate sensor). I know there are already comments in the firmware regarding SPO2 so Gordon might have made a start, but essentially my understanding is SPO2 is calculated using ratios of the AC and DC components of the PPG signal.

In principle yes, but it is probably a tough problem.
Thats the thread for this:
http://forum.espruino.com/conversations/372681/?offset=25#comment16390084
First goal there is to get HRM right when not in rest. But there are people interested in SPO2 and other things to squeeze out of that sensor data. You are invited to participate.

EDIT: oh, same time answer, got interrupted by phone call :-)

As above really - yes, it is possible. The VC31 in KickStarter bangle 2s didn't advertise the capability but the VC31B in the new batch does. As far as I can tell there's not a huge difference though so the first batch may also be fine.

But it's not like there's a 'blood oxygen saturation' value in the sensor that we're just not reading. It has to be calculated from raw data so the value is going to be a bit of a guesstimate.

Guesstimate might be a little bit on the pessimistic side, but certainly there is work to put in both for implementation and validation. I think I remember there is a constant in the calculation that is specific to the PPG device involved, so we will probably need to experiment to determine this, and it may not be the same for the two versions of the HRM.