Update atan second overload value range

glossary/atan/README.md

@@ -22,7 +22,7 @@ vec4 atan(vec4 y_over_x)
 ```y_over_x``` specify the fraction whose arctangent to return.
 
 ### Description
-```atan()``` returns the angle whose trigonometric arctangent is ```y,x``` or ```y_over_x```, depending on which overload is invoked. In the first overload, the signs of ```y``` and ```x``` are used to determine the quadrant that the angle lies in. The values returned by atan in this case are in the range -PI/2 and PI/2. Results are undefined if ```x``` is zero.
+```atan()``` returns the angle whose trigonometric arctangent is ```y,x``` or ```y_over_x```, depending on which overload is invoked. In the first overload, the signs of ```y``` and ```x``` are used to determine the quadrant that the angle lies in. The values returned by atan in this case are in the range -PI and PI. Results are undefined if ```x``` is zero.
 
 For the second overload, ```atan()``` returns the angle whose tangent is ```y_over_x```. Values returned in this case are in the range -PI/2 to PI/2.