High Quality Content by WIKIPEDIA articles! The Hurst exponent is used as a measure of the long term memory of time series. It relates to the autocorrelations of the time series and the rate at which these decrease as the lag between pairs of values increases. Studies involving the Hurst exponent were originally developed in hydrology for the practical matter of determining optimum dam sizing for the Nile river`s volatile rain and drought conditions that had been observed over a long period of time. The name "Hurst exponent" or Hurst coefficient derives from Harold Edwin Hurst (1880–1978), who was the lead researcher in these studies, and the use of the standard notation H for the coefficent relates to this name also.