It was E C Riegel who referred to Value as "the Relativity of Desire".

The problem is that we insist on trying to define the indefinable, confusing "price" (market value) with "value".

Wilde's definition of a Cynic is relevant here.

"Someone who knows the Price of everything and the Value of nothing"

It is the question of the metaphysical assumptions which underpin Economics which is at the heart of the problem.

I build upon Pirsig's "Metaphysics of Quality" (which I call a "Metaphysics of Value" - since Quality, Value, God .....it's all One - or, at least, Not Two!) in order to ask better questions of Reality, and to provide assumptions better able to inform Economics..

So, yes indeed, Value is definable ONLY in relative terms, and by reference to a "Value Unit".

"The future is already here -- it's just not very evenly distributed" William Gibson