The base quarter is the older of the two quarters of [glossary:CPI:622] or [glossary::668] data used in indexing a payment rate or limit or threshold. The [glossary:reference quater:109] of the CPI or PBLCI figure is compared to the base quarter CPI or PBLCI figure to determine the indexation factor to be applied. The base quarter is defined in the legislation and varies according to the amount being indexed.