I read earlier today that the danish King Christian 1. pawned the Orkney- and Shetland islands i the 15th century. These could apparently be bought back today for 58.000 gylden. This made me wonder what methods are being used when converting old currencies to new and what the case is for the gylden and maybe others such as the roman sesterces.
Converting between ancient and modern currencies is generally similar to the method of determining inflation between more recent years. You find the prices of a number of common goods from both eras, such as a loaf of bread, a cotton shirt, or a bushel of apples. If the total of that bundle in AD 100 was 1 sesterces and that same bundle was $15 in 2014 then you could estimate a 1:15 exchange rate for AD 100 sestertii to 2014 dollars.