Johan, no problem. Displaying the scale by showing the total distance from one edge of the display to another is my own invention, and so it is not necessarily obvious that the distance refers to the full size of the display rather than the distance from one end of the line to another, like traditional scales.
But I believe showing the full span distance makes it much easier to estimate distances on screen than trying to figure out how many times a short line displayed in the corner of the screen fits between two points elsewhere. Have you noticed that you can tap the scale to switch between horizontal and vertical distance on screen?
The tutorial video is now being updated to include a little mention about the scale display and how it is used. It should appear on the app's page in Play Store within a week or two.
Thanks for contacting me. I may add a bit of explanation about the scale to the preferences page where the scale can be toggled on and off.
Marko Teittinen
Author of Custom Maps