Purchasing power fluctuates though? FX fluctuates, one is strong one is weak. This is how it works.

Now if you have to measure it you need to measure it FX for FX, i.e. SATs per big Mac or USD per big Mac.

A decline in currency purchase power is different from real stores of value like gold.

Let's look at BTC for instance, at a higher USD value, it's less SATs per burger and inverse if that it goes down, BUT if we priced burgers solely in SATs, what happens? Would it cost more SATs or less SATs over time?