Events in HScrollBar Movement

Question

I am making an windows form app in .net using visual c#

I have added a Hscrollbar on my form.

now i want a button to be visible when i move my bar from left to right

 and i want to my button to be invisible when i move my bar from right to left.

i dont know which event of Bar i should use here.

 

Please Help.. Thanx In Advance