diff --git a/pyndustri.pyi b/pyndustri.pyi
index 44e7809..3fca005 100644
--- a/pyndustri.pyi
+++ b/pyndustri.pyi
@@ -729,6 +729,9 @@ def noise(a: float, b: float) -> float:
 def abs(a: float) -> float:
     """Absolute Value"""
 
+def len(a) -> float:
+    """The magnitude of a vector"""
+
 def log(a: float) -> float:
     """Natural Logarithm"""
 
diff --git a/pyndustric/constants.py b/pyndustric/constants.py
index 3bfe4f1..4379b89 100644
--- a/pyndustric/constants.py
+++ b/pyndustric/constants.py
@@ -85,6 +85,7 @@
     "atan2": 2,
     "noise": 2,
     "abs": 1,
+    "len": 1,
     "log": 1,
     "log10": 1,
     "sin": 1,