Private investors should hold up to 15 percent of their wealth in physical gold, according to a German asset-management company that plans to set up 500 "Gold-To-Go" ATMs in Germany, Switzerland and Austria sometime this year. One of the gold-dispensing ATMs was on display at Frankfurt, Germany's main railway station for a one-day marketing test on Tuesday. A one-gram (0.0353 ounce) piece of gold, the size of a child's fingernail, and about as thin, costs 31 euros (U.S. $42.25) — a 30-percent premium to the market price.