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Table 1 Period of time until documents with a given DP become unfit for use assuming average frequency of use at The National Archives (Kew), i.e. 0.425 times per document per year, and with the threshold of one large missing piece per 100 sheets

From: Damage function for historic paper. Part II: Wear and tear

DP Years to unfit
300 55
400 160
500 450
600 1300
700 3700
800 10,000