The ICSC weekly U.S. retail chain store sales index measures nominal same-store or comparable-store sales excluding restaurant and vehicle demand. The weekly index is constructed using sales-weighted geometric average growth rates to preserve long-term consistency and is statistically benchmarked to a broad-based monthly retail industry sales aggregate that currently represents about 80 retail chain stores, which also is compiled by ICSC. A representative sample of those major retailers has been used as a control group to extrapolate the weekly sales index. As such, the weekly index statistically represents industry sales and is not just a sum of sales for a handful of retailers. The standard period used for the index is Sunday through Saturday, even though some retailers use a different weekly accounting period. The weekly sales index is presented on an adjusted basis to account for normal seasonality and to counter other data anomolies. Weekly seasonal adjustment is at best difficult for chain store sales given that retailers can and often do shift promotions to counter typical shifts in the calendar. Nonetheless, the approach to weekly seasonal adjustment used here follows from the Piser Method, which was popular in the early 1930s and became the standard for weekly adjustment.