The scroll bar control window procedure responds to this message by setting the values of the information range and the position of the slider.

The scroll bar is redrawn to reflect the change.

For example, if a scroll-bar is to allow scrolling through 100 lines of text, of which 50 are visible at any one time, and the top display line is currently number 25, sfirst should be set to 1, slast to 51 (since there are only 51 positions at which the slider may be placed), and sslider to 25. The SBM_SETTHUMBSIZE message should be used in this example to set the slider size to 50 visible parts out of 100.