Modified date

I am using Calibre 3.1.1

Under Preferences there is the option Add your own columns, and you can check the box for Modified. I would expect the latter to show the last date a particular ebook was opened. But that is not not the case. It shows a date later than the download date, but definitely not the date I am looking for.

Is there a way, possibly with a plug-in, to show the last opened date?