weekly sales

[#1]

1)how to create Manual weeks??

i have 1-27 dates

i want

1-7 as first week

8-14 2nd week

15 -21 as 3 rd Week

22-27 as 4th week

in front end

2) and how to create Weekly Sales  for Comparison current Week vs previous week of the month

[MK_QSL]

http://community.qlik.com/blogs/qlikviewdesignblog/2014/01/27/week-numbers