Set Smooth to true to specify that the scroll bar should dynamically adjust its scrolling increment based on the size of the associated control's client area. 

When Smooth is true, clicking the end arrows of the scroll bar scrolls the associated control by approximately one tenth of its client area, and clicking the scroll bar beside the thumb tab scrolls the control by the length of the client area minus the amount scrolled by the end arrows. When Smooth is false, the Increment property controls the amount of scrolling when the user clicks the end arrows, and clicking beside the thumb tab scrolls the control by the entire length of the client area. 

Increment 

Position