diff --git a/src/FocalPointManagerInterface.php b/src/FocalPointManagerInterface.php
index 06c1c05..b1c1dfb 100644
--- a/src/FocalPointManagerInterface.php
+++ b/src/FocalPointManagerInterface.php
@@ -79,10 +79,13 @@ interface FocalPointManagerInterface {
   /**
    * Converts relative focal point coordinates as a crop entity.
    *
+   * Think of the $x and $y arguments as percentages. Using 50 for both $x and
+   * $y would mean to put the focal point in the center of the image.
+   *
    * @param float $x
-   *   X coordinate of the focal point.
+   *   Relative X coordinate of the focal point. Maximum is 100.
    * @param float $y
-   *   Y coordinate of the focal point.
+   *   Relative Y coordinate of the focal point. Maximum is 100.
    * @param int $width
    *   Width of the original image.
    * @param int $height