FactGrid:Coins and Currencies
A brief historical introduction
Calculating with historical sums of money is at first sight a thing for specialists, numismatists. The currencies are obsolete and usually not even organised in decimal systems.
Some things were easier though: Today's currencies are fluctuating in a constant fixing performed on the market that is trading with foreign currencies.
Early modern currencies were metal based, that is the monetary value was basically in the coin: an amount of silver, gold, or copper people would carry around. The coins would wear off over time and the territorial mints would sooner or later replace a particular coin like a silver Shilling with an equivalent coin of a lower silver content thus making money of the constant degradation of the circulating coins; that was basically the constant loss of value everyone had to handle (those with productive capital would do this better than poor people who could only save their money).
Sums of money were usually given in a book currencies independent of the coins circulating: Units like the Reichsthaler and the Pound Sterling had stable fixed silver or gold values while the existing coins would make a varying sum at any given moment. Traders knew the fixed ratios between two currencies like "9 Pound Sterling is 40 Reichstaler" and these ratios remained stable from the 17th into the 18th century. "Bills of exchange" ("Wechsel") would make it unnecessary to carry larger sums of money from one spot to another. You contacted a Merchant with connections to a city you wanted to visit; you gave him the money you want to spend in that other city and he would give you a bill of exchange on which his business partner abroad would give you that very sum in local currency. The merchants in turn could use temporary deficits as assets in their own internal trading.
The system was globally complex with the constant degradation of circulating coinages and the flow of the metals gold and silver between the nations. As soon as a nation had a different fixing of the gold-silver balance the market would create a flow of the undervalued metal into those parts of the world that did not follow the metrics.
Calculate with historical moneys
Calculations with the established exchange rates like the "9 Pound Sterling equals 40 Reichsthaler" are relatively safe between 1650 and 1750. The The Marteau Early 18th-Century Currency Converter offers a tool set.
You can otherwise gain independence with a calculation that converts the sum into silver or gold equivalents. This is relatively safe up to the year 1871 when big players like Germany introduce the Gold standard without taking care of the silver value any longer. Up to that point individual nations could move from gold to silver standards and back with minor economic repercussions - they still remained in a corridor of the global notion of rough equivalents between gold and silver. After the 1860s, however, silver is loosing rapidly against gold, jumping from a ratio of once 1:14 to 1:100. These fluctuations are not yet over, we are still witnessing a good deal of speculation on the gold-silver parity especially with anticipations of the rise and fall of gold on the silver market.
Use SPARQL to convert sums into silver equivalents
FactGrid coins and FactGrid items for the stable book currencies (should all) come with silver and gold equivalents (not to be confused wit the silver content that has its own property) and with date ranges for this information, so that you can use a conversion into the silver equivalent to compare statements of values between currencies and over longer periods of time.
The following search gives the SPARQL-code for a conversion - here of German 19th-century Reichstaler: