diff --git a/docs/lib-shape_arc.md b/docs/lib-shape_arc.md
index d99c5064..42c50d6e 100644
--- a/docs/lib-shape_arc.md
+++ b/docs/lib-shape_arc.md
@@ -5,7 +5,7 @@ Returns shape points of an arc shape. They can be used with xxx_extrude modules
 ## 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.
+- `angle` : A single value or 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`.
 - `$fa`, `$fs`, `$fn` : Check [the circle module](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#circle) for more details.
 
@@ -13,7 +13,7 @@ Returns shape points of an arc shape. They can be used with xxx_extrude modules
 
     include <shape_arc.scad>;
 
-    shape_pts = shape_arc(radius = 10, angles = [-90, 90], width = 5);
+    shape_pts = shape_arc(radius = 10, angle = [-90, 90], width = 5);
     polygon(shape_pts);
 
 ![shape_arc](images/lib-shape_arc-1.JPG)
@@ -27,7 +27,7 @@ Returns shape points of an arc shape. They can be used with xxx_extrude modules
     t_step = 0.05;
     width = 2;
 
-    shape_pts = shape_arc(radius = 10, angles = [180, 360], width = 5);
+    shape_pts = shape_arc(radius = 10, angle = [180, 360], width = 5);
 
     p0 = [0, 0, 0];
     p1 = [40, 60, 35];