The currency moves are the biggest one-day falls in 20 years, and in particular, since China reformed its currency system in 2005. Back then, it unpegged the yuan, also known as the renminbi (RMB), from a strict tie with the dollar in favour of a looser tracking policy. The successive devaluations follow a further shift in policy that means the bank will now expand the criteria used to calculate the daily fix - the rate at which it determines the currency's value each morning and from which it is in theory allowed to move 2 percentage points in either direction, although in practice the moves are much smaller. How can it help the Chinese economy? Chinese businesses compete with regional rivals to supply the world with everything from raw steel to fridges, and a cheaper yuan will make Chinese exports less expensive, potentially boosting the overseas sales that have been among the main drivers of growth during the nation's remarkable rise over the past three decades. However, controls on the currency have given Chinese businesses a high degree of predictability when they plan investments in industries heavily dependent on exports. How can this move help the yuan become a reserve