Aiming to solve this problem, the government banned all forms of non-state-owned internal trade, which they believed to be capitalistic, resulting in an economic crisis so severe that Tố Hữu referred to it as a "vertical downturn".[citation needed] Despite the inflation rates having stabilized as part of the Đổi Mới reforms, especially during the 1990s and early 2000s, the effects of the crisis still last in the value of the dong, one of the lowest in the world today.Prior to its reintroduction, Vietnamese consumers had to exchange banknotes for tokens with a clerk before purchasing goods from vending machines.This was also to help the state ease the cost of producing large quantities of small denomination banknotes, which tended to wear easily.This has prompted laws requiring private and municipal banks to transact and offer services for coins and the full discontinuation of small denomination and cotton-based notes.[20][21] In 1978, the State Bank of Vietnam (Ngân hàng Nhà nước Việt Nam) introduced notes in denominations of 5 hao, 1, 5, 10, 20, and 50 dong dated 1976.Except for the current series, dated 2003, all were confusing to the user, lacking unified themes and coordination in their designs.[29] The one-hundred-dong bill technically remains in circulation, however due to its low value (roughly $0.004 USD) it is rarely ever used for transactions.[citation needed] A commemorative polymer 50 dong banknote dedicated to the fiftieth anniversary of the State Bank of Vietnam was issued in 2001, but its face value is so tiny that it clearly was meant only for collectors.After the use of the Zimbabwean dollar ceased on 12 April 2009,[47] the dong was the second least valued currency unit after the Iranian rial as of 28 November 2014.Since 19 June 2014, the Vietnamese dong has been devalued a total of five times in an effort to help spur exports and to ensure the stability of the currency.