Hebdo

Hebdo- is an archaic decimal metric prefix equal to 10⁷, symbolized by H. It is derived from the Greek hebdοmos (Greek: ἕβδομος) meaning seventh.

The definition of one hebdomometre or hebdometre as 10.000.000 metre was originally proposed by Rudolf Clausius for use in an absolute electrodynamic system of units named quadrant-eleventh-gram-second system (QES system) aka hebdometre-undecimogramme-second system (HUS system) in the 1880s. It was based on the meridional definition of the metre which established 1/10.000.000 of a quadrant, a quarter of an astronomical meridian or the distance from the north pole to the equator, as a metre.