An interesting fact about the Spanish Milled Dollar -- or, more properly, the 8 Reales piece -- is that, due to a lack of fractional coinage (there were 1/2 Real, 1 Real, 2 Real and 4 Real pieces; but most of the silver went into 8 Reales pieces (and gold into 8 Escudo pieces). If you needed change -- you took out a chisel and cut the coin into as many as 8 pieces, or "bits", each worth 1 Real. If you had a quarter of an 8 Reales piece, then, you had 2 Reales, or "two bits".

BTW -- many European countries used coins of this size as a standard. In fact, if you look at David Merrill's avatar, you will see the Maria Theresa Thaler -- so renowned for its weight and purity that it was often imitated by other countries, and was struck by the Austrians well into the 20th century because certain Arab tribes insisted on them, and only them, as a means of exchange.