The difference in paper's moisture content at a particular relative humidity due to changes in the paper's conditioning. The primary constituents of paper, fibers of cellulose, have a strong affinity for water and will gain (or lose) it readily, depending on the amount of moisture in the air. For a particular paper, its moisture content at increasing relative humidities can be plotted on a graph, and a moisture content curve drawn. However, a paper's moisture curve will vary, depending on whether the paper has started at a high relative humidity and then been conditioned to lower relative humidities or whether it has started at a low relative humidity and then been conditioned to higher ones. Thus, two papers of the same type will possess different moisture contents at the same relative humidity depending on its previous "moisture history." This difference, hysteresis, is important when determining a paper's equilibrium moisture content. (See also Moisture Content.)

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