This changes the steps of the speed (MPH or KPH.) The lowest value is 1, and it increments in steps of 5. If the Maximum Number of Lines is exceeded the Step value is increased until the Maximum number of lines is not exceeded.
The number of lines printed will be less than or equal to the maximum lines and is displayed below the trackbar. This displays the number of lines of output by speed; approximately 20 more lines are added for the title and header and footer.
Not very useful on the Lister or the HTML output as there are scroll bars in those, it is more useful on the Printer Output so the font used does not become so small as to be illegible.
You can view the Lister to see the changes.