Meter reading estimation

Hi,

For estimation of meter reading I want know what is the purpose of weighting units (Where key=05) and periodic consumption when estimating a reading?

Say the base category is set as 'Previous period', the minimum portion percent is define as 600% and period length is 20, that is, total of 120 days how the calculation for estimate is done?

Secondly for 120 days, means it will read 120 days in the past! Right? Will it consider only WORKING DAYS as define in SCAL or all?

Thanks for a prompt reply,

Gavisht.