Bug in NumberPlane when using x_max (and likely the y/min values too)
```python
NPac=NumberPlane(x_max=20).add_coordinates()
class Test(Scene):
    def construct(self):
        self.add(NPac.shift([-15,0,0]))
        self.wait(1)
```
This results in the horizontal lines not being anywhere near as long as they should be. Leaving this here for either someone else to investigate or fix, or in case of doubt myself coming back to this some point in the not too close future.
diff --git a/manim/mobject/coordinate_systems.py b/manim/mobject/coordinate_systems.py
index 10b2e2dc..3b2b9466 100644
--- a/manim/mobject/coordinate_systems.py
+++ b/manim/mobject/coordinate_systems.py
@@ -288,6 +288,7 @@ class NumberPlane(Axes):
         self.init_background_lines()
 
     def init_background_lines(self):
+        """Will init all the lines of NumberPlanes (faded or not)"""
         if self.faded_line_style is None:
             style = dict(self.background_line_style)
             # For anything numerical, like stroke_width
@@ -310,6 +311,13 @@ class NumberPlane(Axes):
         )
 
     def get_lines(self):
+        """Generate all the lines, faded and not faded. Two sets of lines are generated: one parallel to the X-axis, and parallel to the Y-axis.
+        
+        Returns
+        -------
+        Tuple[:class:`~.VGroup`, :class:`~.VGroup`]
+            The first (i.e the non faded lines) and second (i.e the faded lines) sets of lines, respectively.
+        """
         x_axis = self.get_x_axis()
         y_axis = self.get_y_axis()
         x_freq = self.x_line_frequency
@@ -327,22 +335,43 @@ class NumberPlane(Axes):
         lines2 = VGroup(*x_lines2, *y_lines2)
         return lines1, lines2
 
-    def get_lines_parallel_to_axis(self, axis1, axis2, freq, ratio):
-        line = Line(axis1.get_start(), axis1.get_end())
-        dense_freq = (1 + ratio)
+    def get_lines_parallel_to_axis(self, axis_parallel_to, axis_perpendicular_to, freq, ratio_faded_lines):
+        """Generate a set of lines parallel to an axis.
+
+        Parameters
+        ----------
+        axis_parallel_to : :class:`~.Line`
+            The axis with which the lines will be parallel.
+
+        axis_perpendicular_to : :class:`~.Line`
+            The axis with which the lines will be perpendicular.
+        
+        ratio_faded_lines : :class:`float`
+            The number of faded lines between each non-faded line. 
+
+        freq : :class:`float`
+            Frequency of non-faded lines (number of non-faded lines per graph unit).
+
+        Returns
+        -------
+        Tuple[:class:`~.VGroup`, :class:`~.VGroup`]
+            The first (i.e the non-faded lines parallel to `axis_parallel_to`) and second (i.e the faded lines parallel to `axis_parallel_to`) sets of lines, respectively.     
+        """
+        line = Line(axis_parallel_to.get_start(), axis_parallel_to.get_end())
+        dense_freq = ratio_faded_lines
         step = (1 / dense_freq) * freq
-
         lines1 = VGroup()
         lines2 = VGroup()
+        unit_vector_axis_perp_to = axis_perpendicular_to.get_unit_vector()
         ranges = (
-            np.arange(0, axis2.x_max, step),
-            np.arange(0, axis2.x_min, -step),
+            np.arange(0, axis_perpendicular_to.x_max, step),
+            np.arange(0, axis_perpendicular_to.x_min, -step),
         )
         for inputs in ranges:
             for k, x in enumerate(inputs):
                 new_line = line.copy()
-                new_line.move_to(axis2.number_to_point(x))
-                if k % (1 + ratio) == 0:
+                new_line.shift(unit_vector_axis_perp_to * x)
+                if k % ratio_faded_lines == 0:
                     lines1.add(new_line)
                 else:
                     lines2.add(new_line)
@@ -429,4 +458,4 @@ class ComplexPlane(NumberPlane):
 
     def add_coordinates(self, *numbers):
         self.add(self.get_coordinate_labels(*numbers))
-        return self
\\ No newline at end of file
+        return self
['manim/mobject/coordinate_systems.py']