You are right - word "absolute" is a "difficult" one, and I did try to be careful on how I use it...
As I said, perception of beauty is absolute to the perceiver (to current state of awareness/understandings/feelings), not absolute in the universal way. (You'll see bellow why I don't agree with "your" definition of word absolute.)
Also, note that I used term "temporarily absolute", with which I meant that even if it's absolute to the perceiver at the moment, in some other moment it might be different, since awareness is not fixed, but kinda slightly fluid. Well, I think awareness alone doesn't change much in a short period of time, but perception of one depends way more than just on current personal (soul's) awareness, it also depends on current state of body (and we know how many things can affect our health and beingness, be it of internal or external origin) and brains (mainly personal thinking capacity & quality, and personal ability in how well we memorize things).
Note also, that none can truly/absolutely prove anything to anyone. We cannot even prove our own very existence to anyone else except to ourselves, and ultimately, it's not proving which matters, but how we "feel" about it. In this sense we could say that...
Our very existence is absolute to us, but relative to others.
I don't think that anything can be "independent of arbitrary standards of measurement", which was shown even in Physic, if I recall correctly, e.g. the one who's just observing the experiment affects the experiment itself (if it's true on quantum level it's also true on any level, even though we might not notice it).
So, nothing in real life is truly/absolutely objective, but always subjective.