Convert from barleycorn to zettameter

Unit Definition (barleycorn)
The Barleycorn is an old English unit of length. The custom of using seeds as units of length or weight is very common in farming societies. In Anglo-Saxon England, where barley was a basic crop, barleycorns played this traditional role. The weight of a barleycorn, later renamed the grain, is the original basis of all English weight systems including the older troy system and the later avoirdupois system. As a length unit, 3 barleycorns were equal to the Saxon ynce (inch). The English foot was actually defined as 12 of these ynces, that is, as 36 barleycorns.

Unit Definition (zettameter)
The zettametre (or zettameter), symbol: Zm, is an SI metric unit of length. 1 zettametre is equal to 1e+21 metres, a very large distance. Not to be confused with a zeptometre.