In the latest effort to devise a credible national currency, Zimbabwe has replaced its dollar with the ZiG, short for Zimbabwe Gold. The new unit is backed by bullion and foreign currency reserves held at the central bank. All told, the ZiG is the country’s sixth attempt at establishing its own currency since 2008, when inflation crossed 500 billion percent, according to International Monetary Fund estimates. Not only did that render it worthless, it turned the unit into a global punchline: US T