Livre tournois replaces Livre parisis
Circulating currency
In France, the livre was worth 240 deniers (the "Tours penny"). The latter were initially minted by the abbey of Saint Martin in the Touraine region of France. Soon after Philip II of France seized the counties of Anjou and Touraine in 1203 and standardized the use of the livre tournois there, the livre tournois began to supersede the livre parisis (Paris pound) which had been up to that point the official currency of the Capetian dynasty.
The livre tournois was, in common with the original livre of Charlemagne, divided into 20 sols (sous after 1715), each of which was divided into 12 deniers.
Between 1360 and 1641, coins worth one livre tournois were minted, known as francs (the name coming from the inscription Johannes Dei Gratia Francorum Rex, [Jean, by the grace of God, King of the French]). Other francs were minted under Charles V, Henry III and Henry IV. The use of the name "franc" became a synonym for livre tournois in accounting.
The first French paper money, issued between 1701 and 1720, was denominated in livre tournois (see "Standard Catalog of World Paper Money", Albert Pick).  This was the last time the name was used officially, as later notes and coins were denominated simply in livres, the livre parisis having finally been abolished in 1667.Accounting currency
With many forms of domestic and international money (with different weights, purities and quality) circulating throughout Europe in the late Middle Ages and the early modern period, the use of an accounting currency became a financial necessity. In the world of international banking of the 13th century, it was the florin and ducat that were often used. In France, the livre tournois and the currency system based on it became a standard monetary unit of accounting and continued to be used even when the livre tournois ceased to exist as an actual coin. For example, the Louisiana Purchase treaty of 1803 specified the relative ratios of the franc, dollar and livre tournois.
The official use of the livre tournois accounting unit in all contracts in France was legislated in 1549, but it had been one of the standard units of accounting in France since the 13th century.  In 1577 the livre tournois accounting unit was officially abolished and accountants switched to the écu, which was at that time the major French gold coin in actual circulation, but in 1602 the livre tournois accounting unit was brought back.  (A monetary unit of accounting based on the livre parisis continued to be used for minor uses in and around Paris and was not officially abolished until 1667 by Louis XIV).
Since coins in Europe in the Middle Ages and the Early modern period (the French écu, Louis, teston d'argent, denier, double, franc; the Spanish doubloon, pistole, real; the Italian florin, ducat or sequin; the German and Austrian thaler; the Dutch gulden, etc.) did not have any indication of their value, their official value was determined by royal edicts.  In cases of financial need, French kings could use the official value for currency devaluation.  This could be done in two ways: (1) the amount of precious metal in a newly minted French coin could be reduced while nevertheless maintaining the old value in livre tournois or (2) the official value of a domestic or foreign coin in circulation could be increased.  By reversing these techniques, currencies could be reinforced.
For example: