What does {:} in columnview specification mean?

Question

A columnview org-columns specification may look like this:

#+BEGIN: columnview :id local :format "%70ITEM(Task) %Effort{:} %CLOCKSUM{:}"
#+END:

Sometimes you can see variations without the {:} part.

What is the function of {:}?

Answer 1

{:} is used to add to the parent nodes a sum of the times for each of the child nodes in the table for that column.

In column views anything in { } is to specify the summary type for that column. : is specifically for times. See SUMMARY-TYPE in the column attributes docs for more info.