 Officials arrested executives of some Zimbabwean companies for increasing prices on their products, and economists reported that "chaos had started to reign and people in the public sector has becoming frantic".On 6 September 2007, the Zimbabwe dollar was devalued again by 92%, creating an official exchange rate of ZW$30,000 to US$1, although the black market exchange rate was estimated to be ZW$600,000 to US$1.As an official exchange rate became more unreliable, the WM/Reuters company introduced a notional exchange rate (ISO ZWN) which was based on Purchasing Power Parity utilising the dual listing of companies on the Harare (ZH) and London Stock exchanges (LN).