Hi Pascal,

M.P. <mattia.pascal@gmail.com> writes:

> I'd like to add to my tasks a property  whose value should be the difference in
> time between the effort estimates and the actual clocked time. The final purpose
> is to use the property in column view mode as I do with CLOCKSUM and Effort.
> Could you give me any hints?

There is no way to do this easily right now.

However, this command will display the remaining effort:

#+begin_src emacs-lisp
(defun my-org-display-remaining-effort ()
  "Compute remaining effort for current subtree."
  (interactive)
  (let ((clocksum (org-clock-sum-current-item))
	(effort (org-duration-string-to-minutes
                  (org-entry-get (point) "Effort"))))
    (message (org-minutes-to-hh:mm-string (- effort clocksum)))))
#+end_src

Also, the attached patch allow to postprocess property values with
custom functions when inserting them with org-set-properties.

Let me know if you find this useful!

Best,