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How to measure a currencies valuation or devaluation in relevance to itself
It's very hard to measure the worth of an abstract concept like money, particularly over long periods of time. In the modern era we have things like the Consumer Price Index (CPI) in the United States, where the Bureau of Labor Statistics literally sends "shoppers" out to find prices of things and surveys people to find out what they buy. This results in a variety of "indexes" which variously get reported by media outlets as "inflation" (or "deflation" if the change in value goes the other way). There are also other measurements available like the MIT Billion Prices Project which attempt to make their own reading of the "worth" of currencies. Those kinds of things are about the only ways to measure a currency's change in "value to itself" because a currency is basically only worth what one can buy with it. While it isn't "all the world's currencies combined", there is a concept of the International Monetary Fund's "Special Drawing Rights (SDR)", which is a basket of five currencies used by world central banks to help "back" each other's currencies, and is (very) occasionally used as a unit of currency for international contracts. One might be able to compare the price of one currency to that of the SDR, or even to any other weighted average of world currencies that one wanted, but I don't think it's done nearly as often as comparing currencies to the basket of goods one can buy to find "inflation". Even though one might think what would be important to measure would be overall Money Supply Inflation, much more often people care more about measuring Price Inflation. (Occasionally people worry about Wage Inflation, but generally that's considered a result of high Price Inflation.) In order to try to keep this on topic as a "personal finance" thing rather than an "economics" thing, I guess the question is: Why do you want to know? If you have some assets in a particular currency, you probably care most about what you'll be able to buy with them in the future when you want or need to spend them. In that sense, it's inflation that you're likely caring about the most. If you're trying to figure out which currency to keep your assets in, it largely depends on what currency your future expenses are likely to be in, though I can imagine that one might want to move out of a particular currency if there's a lot of political instability that you're expecting to lead to high inflation in a currency for a time.