Rebased as of May 2011, new base period is now October 2009 to September 2010. Different series of CPIs are compiled to reflect the impact of consumer price changes on households in different expenditure ranges. The CPI(A), CPI(B) and CPI(C) are compiled based on the expenditure patterns of households in the relatively low, medium and relatively high expenditure ranges respectively. A Composite CPI is compiled based on the overall expenditure pattern of all the above households taken together to reflect the impact of consumer price changes on the household sector as a whole.CPI (A) relates to about 50% of households, in the relatively low expenditure range. Their average monthly expenditure during the new base period of October 2009 to September 2010 was between $4,500 and $18,499.CPI (B) relates to about 30% of households, in the medium expenditure range. These households spent between $18,500 and $32,499 a month in the same base period.CPI (C) relates to about 10% of households, in the relatively high expenditure range. Their monthly expenditure in the base period was between $32,500 and $65,999. History is stored independently for monthly and yearly frequencies. HP values for these frequencies may not match each other. Note that when only one frequency is stored in history, for the other frequencies, history is derived from that of the stored frequency. For example, HP W, HP M, HP Q and HP Y will derive data from HP D when only daily history is stored, HP Q and HP Y will derive data from HP M when only monthly history is stored. As another example, if both daily and monthly are stored, HP W will derive data from HP D, while HP Q and HP Y will derive data from HP M and so on.