diff --git a/docs/lib3x-bezier_curve.md b/docs/lib3x-bezier_curve.md
index 743505fb..998e2690 100644
--- a/docs/lib3x-bezier_curve.md
+++ b/docs/lib3x-bezier_curve.md
@@ -4,7 +4,7 @@ Given a set of control points, the `bezier_curve` function returns points of the
 
 ## Parameters
 
-- `t_step` : The distance between two points of the Bézier path.
+- `t_step` : 0 ~ 1. Control the distance between two points of the Bézier path.
 - `points` : A list of `[x, y]` or `[x, y, z]` control points.
 
 ## Examples
diff --git a/docs/lib3x-curve.md b/docs/lib3x-curve.md
index 0b524e68..4414b831 100644
--- a/docs/lib3x-curve.md
+++ b/docs/lib3x-curve.md
@@ -6,7 +6,7 @@ Draws a curved line from control points. The curve is drawn only from the 2nd co
 
 ## Parameters
 
-- `t_step` : The distance between two points of the generated curve.
+- `t_step` : 0 ~ 1. Control the distance between two points of the generated curve.
 - `points` : A list of `[x, y]` or `[x, y, z]` control points.
 - `tightness` : You can view it as the curve tigntness if you provide a value between 0.0 and 1.0. The default value is 0.0. The value 1.0 connects all the points with straight lines. The value greater than 1.0 or less than 0.0 is also acceptable because it defines how to generate a bezier curve every four control points.