There are strange stories, wild and fairly uninformed rumour I suspect, about the Apple Watch.

When it ships – three words which carry a great deal of meaning and relevance – it is expected to have a range of health-related sensors. Speculation is that these include heart rate, but that Apple has dropped plans to include skin conductivity (or resistance), blood pressure, and oxygen saturation.

For a modest consultancy fee, I could have told Apple that those latter three were not really feasible or worth the trouble and cost. I am sure that their own in-house experts figured this out a good while ago, not just in the last few days or weeks.

Skin conductivity has long been used in Polygraph machines, widely used as ‘lie detectors’. It is not a good measure of ‘stress’ (in fact, if it can be used to estimate anything it is not ‘stress’ but ‘strain’), and has all sorts of issues, as it is dominated by local sweating. A much more promising way to assess ‘stress’ is to analyse heart rate variability, something that several similar biotech devices already do, and which is well reported in the open scientific literature.

Blood pressure is also not a good choice because of the various issues in trying to measure it in such a sensor, and the implications for the many who do suffer from high blood pressure when measured accurately. A wrist-mounted sensor would be a loser from the start.

Oxygen saturation could be measured, but requires a lot of power, and would only change much in someone with a medical condition (or at extreme altitude). Even during exercise, it would be a waste of space and cost to try, in my opinion.

I am puzzled as to why this story has appeared now – surely Apple would have these things figured out months or years ago.