Floating And Fixed Exchange Rates
by Reem Heakal
Some governments may choose to have a "floating," or "crawling" peg, whereby the government reassesses the value of the peg periodically and then changes the peg rate accordingly. Usually the change is devaluation, but one that is controlled so that market panic is avoided. This method is often used in the transition from a peg to a floating regime, and it allows the government to "save face" by not being forced to devalue in an uncontrollable crisis.
Source: http://www.investopedia.com/articles/03/020603.asp