Unity Script Reference:

static function DrawWireArc(center: Vector3, normal: Vector3, from: Vector3, angle: float, radius: float): void;

static void DrawWireArc(Vector3 center, Vector3 normal, Vector3 from, float angle, float radius);

static def DrawWireArc(center as Vector3, normal as Vector3, from as Vector3, angle as float, radius as float) as void

Parameters

center	The center of the circle.
normal	The normal of the circle.
from	The direction of the point on the circle circumference, relative to the center, where the arc begins.
angle	The angle of the arc, in degrees.
radius	The radius of the circle Note: Use HandleUtility.GetHandleSize where you might want to have constant screen-sized handles.

Description

Draw a circular arc in 3D space.

Wire Arc in the Scene View.

	// Create a 180 degrees wire arc with a ScaleValueHandle attached to the disc
	// that lets you modify the "shieldArea" var in the WireArcExample.js
	
	@CustomEditor (WireArcExample)
	class DrawWireArc extends Editor {
	    function OnSceneGUI () {
	    	Handles.color = Color.red;
	        Handles.DrawWireArc(target.transform.position, 
				target.transform.up, 
				-target.transform.right, 
				180, 
				target.shieldArea);
	        
	        target.shieldArea = 
			Handles.ScaleValueHandle(target.shieldArea,
	        				target.transform.position + target.transform.forward*target.shieldArea,
	        				target.transform.rotation,
	        				1,
	        				Handles.ConeCap,
	        				1);
	    }
	}

And the script attached to this Handle:

	// WireArcExample.js
	
	var shieldArea : float = 5;