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An zeptometer is a unit of length, a combination of the metric prefix zepto (symbol z) and the SI unit of length meter (symbol m), equal to 10−21 meter or 1.0E-21 meter and its symbol is zm. Plural name is zeptometers.
The barleycorn is a small English unit of length equal to 1⁄3 of an inch (i.e., close to 0.8467 cm) still used in Great Britain and Ireland as a determiner of shoe sizes.