motion/core_ext/date_and_time/calculations.rb
def prev_week(start_day = Date.beginning_of_week)
      first_hour{ weeks_ago(1).beginning_of_week.days_since(days_span(start_day)) }
    end
def prev_week(start_day = Date.beginning_of_week)
      first_hour{ weeks_ago(1).beginning_of_week.days_since(days_span(start_day)) }
    end
Returns a new date/time representing the given day in the previous week.
 Week is assumed to start on +start_day+, default is
 +Date.beginning_of_week+ or +config.beginning_of_week+ when set.
 DateTime objects have their time set to 0:00.