Auditing average user session duration report

Hi all

I want to create a Web Intelligence report based on the BI4 Auditing universe where you can extract how long the user was in average logged in in the BI launchpad (session duration).

Because such a dimension or measure field is not provided by the universe I would like to know how this can be achieved?

If I create a query and set a filter for Event Type EQ "Logon;Logout" the output is as follows:

According this information, I want to evaluate for example the average session duration of the users were in a month.

Furthermore is somebody able to explain me why there are sometimes several logout events captured?

Kind regards

Silvan