The Big Mac Index
In the 1980's the Economist came up with the "Big Mac" index to gauge the true value of a currency.
Their reasoning was as follows: because MacDonalds makes Big Macs around the world to the exact same standards using the same ingredients, the prices should be the same. That is, if you converted the local price of a Big Mac into dollars at market exchange rates, it should be roughly the same price as an American Big Mac.
If when the local currency was converted into dollars, it was higher than the American cost, the local currency must be overvalued (it's buying too many dollars). And vice versa.
Of course it's not an exact science as local factors come into play (e.g. easy availability of beef), but it's a good rough and ready gauge.
Here is the current Big Mac index as of Jan 2024 compared to a eurozone Big Mac:
The Swiss Franc looks way overvalued, and the Japanese Yen looks way undervalued. That means both currencies are likely to see corrections in the year ahead.