property ScrollBar.hWndMouseWheel as Long
Associates a window with the current scroll bar when using the mouse wheel over or while it is focused.

TypeDescription
Long A Long expression that specifies the handle of the window to be associated with the current scroll bar. If -1, the mouse wheel works anywhere on the form, or the scroll bar's value is changed every time the user rolls the mouse wheel, no matter what field is focused.
By default, the hWndMouseWheel property is 0, which indicates no window associated with the scroll bar. If non-zero, this property indicates that handle of the window to be associated with the current scroll bar, so while this window has the focus, rotating the mouse wheel will be forward to the scroll bar to change the current value. For instance, let's say we have a text-box and we want to be able to change the value inside while the user rotates the mouse wheel.