From Xojo Documentation
The scrollbar control.
A Scrollbar can be either horizontal or vertical. To set its orientation programatically, set the height to be greater than the width for a vertical scrollbar. Set the width to be greater than the height for a horizontal scrollbar. The default thickness of the short side is 16 pixels, but it can be changed. You can narrow it in the IDE to get a mini-scrollbar.
Changing the maximum value of a Scrollbar at runtime:
Setting the text of a Label, control to the value of the Scrollbar when the user scrolls:
See also the discussion of scrolling ListBox controls horizontally using a Scrollbar control.