diff --git a/movecenter.md b/movecenter.md
index 9b2d060..67161b0 100644
--- a/movecenter.md
+++ b/movecenter.md
@@ -7,6 +7,14 @@ It does NOT uncenter the window back to its previous location. It does not cente
 
 The variable `center_relative_to_monitor` allows the user to choose whether to center relative to the monitor or relative to the window area.
 
+<details>
+<summary>Explanation of center_relative_to_monitor:</summary>
+<pre>
+The "Monitor area" refers to the space enclosed by the green rectangle, while the "Window area" refers to the space enclosed by the red rectangle.
+<img src="https://i.imgur.com/xhejzPh.png"/>
+</pre>
+</details>
+
 ### Download
 - [2023-09-11](https://github.com/djpohly/dwl/compare/main...wochap:movecenter.patch)