A feature of some <a href="search.pl?p=exponential smoothing">exponential smoothing</a> programs that allows the user to specify the time of one or more special events, such as irregular promotions and natural disasters, in the <a href="search.pl?p=calibration data">calibration data</a>. For each type of special event, the effect is estimated and the data adjusted so that the events do not distort the trend and seasonal patterns of the time series. Some programs use a procedure called <a href="search.pl?p=intervention analysis">intervention analysis</a> to model events.<o:p></o:p></P>