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docs/lib-arc.md

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+# arc
+
+Create an arc. You can pass a 2 element vector to define the central angle. It provides a `fn` parameter consistent with the `$fn` parameter of the circle module. It depends on the `circular_sector` module so you have to include circular_sector.scad.
+
+## Parameters
+
+- `radius` : The radius of the circle.
+- `angles` : A 2 element vector which defines the central angle. The first element of the vector is the beginning angle in degrees, and the second element is the ending angle.
+- `width_mode` : The default value is `LINE_CROSS`. The arc line will move outward by `width /2` and inward by `width / 2`. If it's `LINE_OUTWARD`, the arc line moves outward by `width`. The `LINE_INWARD` moves the arc line inward by `width`.
+- `fn` : The `$fn` value used by the `circle` module internally. The default value is 24.
+
+## Examples
+
+    arc(radius = 20, angles = [45, 290], width = 2);
+    %circle(r = 20, $fn = 24); 
+
+![arc](images/lib-arc-1.JPG)
+
+    arc(radius = 20, angles = [45, 290], width = 2);
+    %circle(r = 20, $fn = 24); 
+
+![arc](images/lib-arc-2.JPG)
+
+    arc(radius = 20, angles = [45, 290], width = 2, width_mode = LINE_OUTWARD);
+    %circle(r = 20, $fn = 24); 
+
+![arc](images/lib-arc-3.JPG)
+