[Excerpt] Every year, certain industries experience substantial seasonal variations in their business activity. In other words, they have strong seasonal hiring and laying off patterns. During these periods, which can last for months, affected industries buildup the number of employees, to accommodate the increased seasonal activity. One of the most notable buildup periods occurs in retail trade for the winter holiday season, which falls in the last 3 months of the year. Knowing that this seasonal activity takes place each year, a “buildup” table can be used to help gauge the level of seasonal hiring compared with previous years and also can be used to explain trends in employment after seasonal adjustment.