That looks statistical analysis of some kind, it gives this example: > the onset of the COVID-19 outbreak, lowered emotional well-being by 74%.

So it's not like it can assess this number for an individual, at least not without first comparing and contrasting it with every other person in some sample group.

In other words, a true unit of happiness, would allow a completely independent measure of any one individual's current state of happiness. Imagine something like a thermometer for happiness, you point it at someone and it reads out the units of happiness (over-simplifying the application to make the point). Therefore we're not even close to knowing what this is or how to measure it, and the way we really communicate around it is by using our own subjectivity of it and making correlations.