In Europe paper money was first introduced in Sweden in 1661. Sweden was rich in copper, thus, because of copper's low value, extraordinarily big coins (often weighing several kilograms) had to be made. Because the coin was so big, it was probably more convenient to carry a note stating your possession of such a coin than to carry the coin itself.

Bollinger Bands are one of the most popular technical analysis techniques. The closer prices move to the upper band, the more overbought is the market, and the closer prices move to the lower band, the more oversold is the market.

PPI - Producer Price Index; Core-PPI. Bureau of Labor and Statistics; the second full week of each month, 8:30am EST, covers previous month data.