From Thomas Jefferson Encyclopedia
Thomas Jefferson came of age in a confusion of currency. The gold and silver of many kingdoms filled the gap created by a chronic scarcity of British coins in the American colonies. Jefferson's Memorandum Books reveal that he loaded friends bound for England with precious metal of all shapes and nationalities. In 1769 he handed Matthew Maury, seeking books for Jefferson and ordination for himself in London, three gold Portuguese half johannes (joes), two gold German ducats, and a silver coffeepot, weighing twenty-two ounces. A year later, one of Jefferson's most troublesome legal clients finally paid him in a motley mixture of silver and gold -- half joes and moidores from Portugal, doubloons and pistoles from Spain, and 308 English half crowns.
To compound the disorder of the situation, each colony had its own rates of exchange. On crossing the border from Virginia to Maryland in 1775, Jefferson had to note in his Memorandum Book the new values of Spanish dollars and pistareens and Portuguese half joes, as well as English guineas and shillings. But for Jefferson, even a purely British system would have been an ordeal. He described the mysteries of arithmetic for an American school boy, "puzzled with adding the farthings, taking out the fours and carrying them on; adding the pence, taking out the twelves and carrying them on; adding the shillings, taking out the twenties and carrying them on."
"But when he came to the pounds," Jefferson continued, "where he had only tens to carry forward, it was easy and free from error." Jefferson began advocating decimal reckoning as an orderly alternative to the currency chaos in 1776. In 1784, after his "Notes on the establishment of a Money Unit," he recommended a system with the advantages of convenience, simplicity, and familiarity. The Spanish dollar was convenient in size, its decimal division would make computation simple, and its multiples and subdivisions would accord with already well-known coins. "Even mathematical heads," he admitted, "feel the relief of an easier substituted for a more difficult process." Jefferson's lucid arguments overwhelmed rival plans and the United States soon became the first nation in history to adopt a decimal coinage system.
--Original author: Lucia C. Stanton, Monticello Research Department. Condensed from an essay printed in the Monticello Newsletter 5:(Summer 1994).