The most difficult information to determine when researching Dutch-Paris was not figuring out what happened in a clandestine network that reached across five countries or the names of the people involved – although that required research in over 30 archives in five languages – but how much things cost during the Second World War.

There are a lot of prices quoted in the documents. A train ticket between Lyon and Annecy cost 80 French francs. A rucksack on the black market in Toulouse cost 280 French francs. The Dutch embassy in Switzerland routed 30,000 Swiss francs to the rescuers in Brussels. Meneer X gave Monsieur Y 120 Dutch guilders. But how much are any of those figures actually worth? How many Belgian francs would Swiss francs get on the black market and how much could they buy on the black market? And how does that convert to the Euro or Dollar today?

I’ve consulted economic historians who specialize in historical currency conversion. The best they can tell me is that they can’t tell me. The war changed the world economy in many ways, including how governments everywhere suspended the free market in favor of controlling natural resources with military uses, transportation and food. The Nazis certainly did all that in addition to imposing artificial exchange rates in all the territories that they occupied. It hardly needs to be said that those exchange rates were extremely favorable to Germany. Furthermore, the occupation authorities kept a strict eye on both the currency and commodities exchanges. In fact, the Treasury department of the Third Reich had its own armed unit called the Devisenschutzkommando (DSK or currency protection command) whose members monitored the flow of money and valuables across borders. They had the power to hunt down Jews in order to steal their valuables on behalf of the Third Reich, and they did so.

his means that looking at official currency exchange rates during the Occupation is meaningless if you are interested in the daily lives of civilians. That’s why economic historians tell me that if you want to try to figure out the value or cost of an item you must forget the exchange rates and try to determine what that item could have been exchanged for. If you want to know how much a pair of shoes cost, you need to answer not in French francs but in staples such as loaves of bread. At any given time or place, what would a consumer have had to trade to get those shoes? If the answer is a certain amount of cash, then all you know about the value of that cash is that at that time and place it was worth a pair of shoes.

Prices changed with time and circumstances. An apple, for instance, would naturally cost more in March than it would at harvest time in September. That same apple would cost much more in a big city like Paris than it would in an apple growing region such as Normandy. The sudden appearance of an invading army on the beaches of Normandy and onslaught of military hostilities there would naturally drive the price of everything up, including apples. But so would a crackdown by the local Gestapo anywhere.

The point is that the war and occupation fractured the national markets into highly volatile local markets. Not only local markets, but illegal clandestine markets. Trading on the black market was always a criminal offense, even if the German authorities themselves did it in Paris. So naturally, it’s not terribly well documented. Given the German interest in controlling currency, the black market in currency was especially dangerous and therefore profitable and therefore attractive to criminals. No wonder economic historians treat Second World War currency exchange rates as a terra incognita.