View Comparison only shows on selected product

The ability to view a comparison, is only available on products that have been selected.
It should be available for view at any stage of the browsing process.
This means that to view the selection, one has to add the presently viewed product to the comparison list, so the “view comparison” button is displayed, so they can click on it to see the comparison (and probably want to remove the last added product).

The visitor could even be prompted with pop-up or side notice, that their selection of choices (option for alternative name) is currently empty, and they can make their selections by pressing the “whatever” button.