lstBox.Items.Count-1 is the value of the
last subscript (index) because the list starts at 0.
If no item is highlighted, the value of SelectedIndex is –1.
hsbBar.Value is a number between
hsbBar.Minimum and hsbBar.Maximum determined by the position of the left of
the scroll box. If the left side of the scroll box is halfway between the two
arrows, then hsbBar.Value is a number halfway between hsbBar.Minimum and hsbBar.Maximum.