From Zak Newman's June 28, 2028 log in the time travel novel Saving JFK.
“Dr. Currant spent the first hour explaining the some of the basics of life in the early 1960s. He has purchased quite a few rare gold and silver coins as well as about ten pounds of common gold coins dating back to the beginning of the 20th century. Since he is a registered numismatist, he is allowed to make such a transaction without causing a fuss with MOM. These, he will exchange for dollars once we arrive. We’re familiar with the idea of dollars. They’re similar in concept to the exos that we use today, except they are paper, not electronic. But understanding the smaller coins is a challenge. The pennies, nickels, dimes, quarters, and half-dollars are what Dr. Currant calls “pocket change.” For my money, carrying these coins around will only create holes in my pocket. I actually like our decimal system of today, although very few transactions involve transferring a part of an exo. A single exo doesn’t buy much and part of an exo buys even less. But A.C. assures us that these nickels and dimes will, in themselves, have some pretty hefty purchasing power in 1963. He’s also bringing some cut diamonds. These, of course, are synthetic. Today, diamonds are just another commodity, like wheat or oil, because of the low cost of creating them. According to Dr. Currant, experts today can’t tell the difference between the real and the synthetic. The synthetic stones are cheap now, but in 1963 diamonds were very valuable and only available in their natural state. They’re small, easy-to-carry, concentrated wealth and they’ll be no problem to sell to the right buyer, says Dr. Currant.”