Short of entering the numbers into a Spread-sheet, I have not found a way to do it.
The reason is simple. This number appears to be a MAJOR justification used by Sleep Clinics (in testing) and Doctors to determine that you need some kind of therapy, and the success of that therapy -- but there doesn't seem to be a mechanic for monitoring this number.
Of course, my experience so far has been that the Doctor doesn't believe in numbers, but just in "do I feel better" using the device than not using it.
I don't disagree (completely) with that approach, but being and Engineer, it really bothers me.
Retired computing and networking professional
(ARPAnet, Unix and Mac OSX)
"People assume that time is a strict progression of cause to effect,
but actually — from a non-linear, non-subjective viewpoint —
it's more like a big ball of wibbly-wobbly... timey-wimey... stuff."