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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.
An ell (from Proto-Germanic *alinō, cognate with Latin ulna) is a unit of measurement, originally a cubit, i.e., approximating the length of a man's arm from the elbow ("elbow" means the bend or bow of the ell or arm) to the tip of the middle finger, or about 18 inches (457 mm); in later usage, any of several longer units.