diff --git a/manimlib/mobject/geometry.py b/manimlib/mobject/geometry.py
index f0604412..6eebf6b4 100644
--- a/manimlib/mobject/geometry.py
+++ b/manimlib/mobject/geometry.py
@@ -636,6 +636,10 @@ class Arrow(Line):
             super().scale(length / self.get_length())
 
         self.rotate(angle_of_vector(vect) - self.get_angle())
+        self.rotate(
+            PI / 2 - np.arccos(normalize(vect)[2]),
+            axis=rotate_vector(self.get_unit_vector(), -PI / 2),
+        )
         self.shift(start - self.get_start())
         self.refresh_triangulation()
 
diff --git a/manimlib/mobject/number_line.py b/manimlib/mobject/number_line.py
index bd475215..ed6a1ede 100644
--- a/manimlib/mobject/number_line.py
+++ b/manimlib/mobject/number_line.py
@@ -57,6 +57,7 @@ class NumberLine(Line):
         super().__init__(self.x_min * RIGHT, self.x_max * RIGHT, **kwargs)
         if self.width:
             self.set_width(self.width)
+            self.unit_size = self.get_unit_size()
         else:
             self.scale(self.unit_size)
         self.center()
@@ -123,7 +124,7 @@ class NumberLine(Line):
         return self.point_to_number(point)
 
     def get_unit_size(self):
-        return (self.x_max - self.x_min) / self.get_length()
+        return self.get_length() / (self.x_max - self.x_min)
 
     def get_number_mobject(self, x,
                            number_config=None,