Convert from keel [coal] to obol, obolos, obolus [Greece]

Unit Definition (keel [coal])
The keel is a traditional British unit of weight for coal. After considerable variation, the keel of coal was standardized in 1695 as 21.2 long tons, or 47 488 pounds (21.5402 metric tons). This is the approximate weight of coal carried at that time by barges on the river Tyne in northern England; the barges were also called keels, from the Dutch word kiel for such a ship.

Unit Definition (obol, obolos, obolus [Greece])
The obol, obolos, obolus [Greece] is a historic unit of weight or mass. The obol is a very small weight that originated as the weight of a tiny Greek coin. In modern Greece, the obolos is an informal name for the decigram (0.1 gram).