All qualia are grounded in physical, measurable phenomona. How directly and precisely one measures it is a function of technical capability.
Moreover, whatever "ruler" you might wish to use, all that can result is yet another description of "it" - a quantization of a continuum of such measurements - and does not tell us what "it" is until we actually and directly experience "it".
Or to put it another way, one can describe an animal until he is blue in the face - develop vast piles of data comparing the animal to all kinds of other things - and still not know what the animal "is".