Fold number refers to how many
double folds that are required to cause rupture of a paper test piece under standardized conditions. Fold number is defined in ISO 5626:1993 as the
antilogarithm
In mathematics, the logarithm of a number is the exponent by which another fixed value, the base, must be raised to produce that number. For example, the logarithm of to base is , because is to the rd power: . More generally, if , then ...
of the mean folding endurance:
where ''f'' is the fold number, ''F
i'' is the folding endurance for each test piece and ''n'' is total number of test pieces used.
In the introduction of ISO 5626:1993 it is emphasized that fold number, as defined in that very International Standard, does not equal the mean number of double folds observed. The latter is however still the definition used in some countries.
[ISO 5626:1993 Paper – Determination of folding endurance, Introduction.] If the numerical value of the folding endurance is not rounded off, these will however be equal.
In the former Swedish standard SS 152005 ("Pappersordlista") from 1992, with paper related terms defined in Swedish and English, fold number is explained as "the number of double folds which a test strip withstands under specified conditions before a break occurs in the strip"; that is, ''not'' the antilogarithm of the mean folding endurance.
See also
*
Folding endurance In paper testing, folding endurance is defined as the logarithm (to the base of ten) of the number of double folds that are required to make a test piece break under standardized conditions:ISO 5626:1993 Paper – Determination of folding endur ...
*
Double fold
''Double Fold: Libraries and the Assault on Paper'' is a non-fiction book by Nicholson Baker that was published in April 2001. An excerpt appeared in the July 24, 2000 issue of ''The New Yorker'', under the title "Deadline: The Author's Despera ...
References
{{DEFAULTSORT:Fold Number
Paper
Materials testing