Everytime I move the slider bar in my dialog OnHScroll gets called 3 times instead of 1

You're getting WM_HSCROLL messages with different scroll codes (wParam's). You're probably receiving SB_THUMBPOSITION, SB_THUMBTRACK and SB_ENDSCROLL.

From VC++ online help:

SB_BOTTOM
Scrolls to the lower right.

SB_ENDSCROLL
Ends scroll.

SB_LINELEFT
Scrolls left by one unit.

SB_LINERIGHT
Scrolls right by one unit.

SB_PAGELEFT
Scrolls left by the width of the window.

SB_PAGERIGHT
Scrolls right by the width of the window.

SB_THUMBPOSITION
Scrolls to the absolute position. The current position is specified by the nPos parameter.

SB_THUMBTRACK
Drags scroll box to the specified position. The current position is specified by the nPos parameter.

SB_TOP
Scrolls to the upper left.

/ravi