diff --git a/assets/scripts/utils/maths.js b/assets/scripts/utils/maths.js
index 3d441e6..0e2e621 100644
--- a/assets/scripts/utils/maths.js
+++ b/assets/scripts/utils/maths.js
@@ -28,7 +28,7 @@ const lerp = (x, y, a) => x * (1 - a) + y * a
  * @return {number} inverted lerp value
  */
 
-const invlerp = (x, y, a) => clamp((v - x)/(a - x))
+const invlerp = (x, y, a) => clamp((a - x)/(y - x))
 
 
 /**