I need some help drawing an oscilloscopes, VC++

[Todos]

Hello,
Im working with an ultrasonic device and I need to draw a real time wave signal (like an oscilloscope) on a windows form application, I've finished that part but the drawing is to slow, when I move or rezise the drawing gets as faster as I want, so I think it isn't a code problem.

This is the code:

  
public: void draw_scope(unsigned char* data){
	int i=0, x1=0, y1=255;
	float prop;
	Graphics* g = scope->CreateGraphics();
	Pen* myPen = new Pen(Color::Red);  				
	myPen->Width = 1;
	prop =  (float)scope->Width/TBuffer;
	g->ScaleTransform(prop, 1.0f ); 
	g->Clear(Color::White);

	for (i=0; i<TBuffer; i++) //TBuffer can be from 1 to 8190
	{   
		g->DrawLine(myPen, x1,y1 ,i , data[i]); 
		x1=i;
		y1=data[i]; 
	}
}

I'm using a timer to call this function (200ms interval), scope is a PictureBox and the timer is activated before the complete signal is plotted.

Any kind of help is welcome, thank you.

PS: Please excuse my english ;<.
PS2: I'm using .net 2003.