There's no such thing as an objective measurement in macroeconomics. You're always measuring from some normative frame. In other words, relative to what you think *ought* to be true about the world.

There's no such thing as objective value. There's no such thing as objective measure of inflation (no, seriously).

Prices emerge from our preferences. Value emerges from our sentiments.

Sound money doesn't change this. Because the whole concept of sound money emerges from a normative foundations, on how money ought to work. Why should money retain its value across time and space? The only reason is because we all want it to! Not because that's objectively more efficient.