In Zimbabwe, the black-market exchange rate is nearly ten times the official one.

ECONOMIST: Zimbabwe

Venezuela Keeps Official Exchange Rate Despite Flourishing Currency Black Market Trade.

CENTERFORSECURITYPOLICY: Venezuela Brief: Countdown to Tyranny I

The government has abolished jail terms for those caught dealing in foreign currency, offered extra incentives for private investment and brought the official exchange rate closer to the black-market one.

ECONOMIST: Syria

It has led to an increase in currency sales on the black market - but Paypal's exchange rates are better.

BBC: Paypal suspends domestic transactions in Argentina

Now, dollars sell on the black market at three times the official exchange rate and Maduro has had to devalue Venezuela's currency, the bolivar, twice this year.

NPR: Tensions Up In Venezuela After Polls Close

In the 1980s when Iran's foreign currency reserves dried up, licensed exchange bureaux closed down and the black market was run by the street money-changers of Tehran's Ferdowsi Street.

BBC: Iran currency crisis: Sanctions detonate unstable rial

This action targets those people that have been using credit cards as a way to purchase at the official rate rather than the black market rate, in effect creating a dual credit card exchange regime.

FORBES: Argentina Begins Tracking All Credit Cards

Last week, the black box investors at Boston quant fund ClearStream Investments said the big emerging market exchange traded funds were all a buy.

FORBES: The Black Box Says Sell Equities, Keep the Change

With hyperinflation, a gap of around 10:1 has opened up between the official exchange rate operated by the bank and the true rate reflected in the black market.

ECONOMIST: How to prop up the government

The wizard inside the black box over at Boston quant shop ClearStream Investments has opted in to emerging market exchange traded funds after being cash only for nearly a month.

FORBES: Boston Quant Fund Buys the Big EMs As Equities Sink