A hotch-potch of definitions and glosses from different contexts. For the classical Athenian double-drachm see e.g. ?Aristotle, Athenaion Politeia 10.2. Unciae (whence modern ounces) are Roman. "20 obols" -- rather than 12 -- reflects the payments (in shekels) to the temple in Jerusalem in the Septuagint: Leviticus 27.25, Numbers 3.47, etc. For gra/mma as scruple see LSJ s.v., II.5. (As the scruple was one twenty-fourth of an ounce, the figure six with it here is obviously faulty.)
[1] Thus far, same material in other lexica.