diff --git a/src/main/java/de/neemann/digital/draw/graphics/VectorInterface.java b/src/main/java/de/neemann/digital/draw/graphics/VectorInterface.java
index 6d4a45dad..78ac641fc 100644
--- a/src/main/java/de/neemann/digital/draw/graphics/VectorInterface.java
+++ b/src/main/java/de/neemann/digital/draw/graphics/VectorInterface.java
@@ -98,6 +98,9 @@ public interface VectorInterface {
     VectorInterface getOrthogonal();
 
     /**
+     * Calculates the scalar product
+     *
+     * @param v the vector to multiply with
      * @return the scalar product
      */
     default float scalar(VectorInterface v) {