Not really an issue, more of a theoretical/technical question.
I'm doing regional maps with over 1500 km difference (~10 degrees of latitude) between lower/upper border of the map, and I noticed that scale in print composer is fixed and does not change if you move scalebar within composer. So how is it calculated? Is it taking an average scale of the referenced map? A 100 km section(length) of the scalebar on the south would only equal ~80(?) km if moved to the north.