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For the period 1825-1902 (inclusive) the prices are recorded every fortnight; that is to say every two weeks.
For the period 1904-1913 the prices are recorded every month.
1903 is a transition year (mixed fortnight-month).

The records should be read as follows.

 AISNE             SOISSONS
1825  1275 1347 1307 1350 1347 1347 1340 1395 1353 1320 1400 1450
      1347 1407 1552 1555 1519 1525 1576 1558 1596 1690 1697 1696

AISNE is the department (i.e. administrative division) in which the market is located.
SOISSONS is the name of the city in which the market was held.
1825 is the year.

The prices are expressed in centimes (one centime=1/100 franc) per hectoliter.

1275 is the price in the first fortnight of January (Jan. 1 to Jan. 15)
1347 is the price in the second fortnight of January (Jan. 16 to Jan. 31)
1307: price in the first fortnight of February, etc.

Source: French National Archives (Paris)

The data were provided to EH.Net by Bertrand Roehner and published in:

S. Drame, C. Gonfalone, J. Miller, and B. Roehner: Un siecle de commerce du ble en France [Wheat trade and wheat prices in France: 1825-1913]. Economica. Paris (1991)