Scid vs PC, how to get ECO data ? Installed SCID vs PC.
Can this give a count or frequency distribution of the ECO codes of the games ?
So far unable to do this.
Under the Tools tab there is a selection "Opening Report".
This gives a lot of data, most of limited value, such as oldest games, most frequent players, shortest wins. Finally there is 5. Theory Table.
This is a table of moves in 8 columns and 20 double rows. How to interpret this is obscure and certainly not intuitive. 
There is a Help Index.  "Theory table" is absent from Help.

Under Options there is a selection "Load ECO file". Found .eco in data subdirectory of bin. Loaded it. Seems to get me nothing.
You can get a count of how many of a particular ECO code (or a particular range of codes) is in the database.

In the Game List, select Change Filter (magnifying glass icon), then Search by Header (binoculars icon). In the dialog box that pops up, there are two fields for ECO code, allowing you to choose a start and end. For example, enter B00 and B99 if you want to count all the B codes. Then click the Search button. The Game List will now show the count of games in the database that match the filter.