Agenda span of "last 7 days"

Question

I write my weekly report on Wednesdays. As such I need to see what I've done starting last Wednesday until now. (usually a Wednesday).

I would like to create an Agenda view for this, so I can quickly flick between the weeks, but I cannot find a way of specifying '-7' days.

I tried customizing org-agenad-custom-commands and setting the days to '-7' but that only shows the current day.

At present I generate a report for this:

#+BEGIN: clocktable :tstart "<-6d>" :tend "<now>" :scope agenda-with-archives :narrow 70 :formatter my-org-clocktable-notodo :maxlevel 3 :fileskip0

But I can't find a way to transpose this to an Agenda custom view. Is this possible?

[Edit solution]
As per lawlist's advise in the comment I got it to work.

1) I customized org-agenad-custom-commands, added an agenda view that shows "Number of days in agenda" = 8. I assigned "W" to this agenda view.

 '(org-agenda-custom-commands
   ....
     ("W" "Last 8 days." agenda ""
      ((org-agenda-span 8)
  ...

2) I then defined a function that temporarily defines the variable:

(defun my/agenda-last-week () 
  (interactive)
  (let ((org-agenda-start-day "-7d"))
       (org-agenda nil "W"))
)

I then assign a hotkey to that function.

Now I can view my last week Wednesday to Wednesday, (inc time-report). I am happy.

Answer 1

The variable org-agenda-start-day can be used to achieve the behavior desired by the original poster. The doc-string provides as follows:

Start day for the agenda view.
Custom commands can set this variable in the options section.
This is usually a string like "2007-11-01", "+2d" or any other
input allowed when reading a date through the Org calendar.
See the docstring of `org-read-date' for details.

The manual -- https://www.gnu.org/software/emacs/manual/html_node/org/Weekly_002fdaily-agenda.html -- contains the following example: You can also set the start date using a date shift: (setq org-agenda-start-day "+10d") will start the agenda ten days from today in the future.