When calculating weekly averages the system works in two ways.
When calculating averages from "this week", the system will take the value from the day you are currently in and the values up to and including the Monday just gone. For example if it's Friday the 24th, the system will take information from Monday the 20th (Monday just gone) to Friday the 24th (today) inclusive.
When calculating averages for the "previous week" the system will take values from the the Sunday just gone and the Monday previous. For example if it's Friday the 24th, the system will take information from Sunday the 19th (Sunday just gone) to Monday the 13th inclusive.