From e6bc53307daa0518930a11034b13ae91ef8caf84 Mon Sep 17 00:00:00 2001
From: CharlesCNorton <135471798+CharlesCNorton@users.noreply.github.com>
Date: Tue, 8 Sep 2026 18:09:36 -0400
Subject: [PATCH] Describe b0 as the on-axis R B_phi over the axis major radius
 at phi = 0

---
 src/vmecpp/__init__.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/vmecpp/__init__.py b/src/vmecpp/__init__.py
index f76b4e338..49dae4585 100644
--- a/src/vmecpp/__init__.py
+++ b/src/vmecpp/__init__.py
@@ -1953,7 +1953,8 @@ class Threed1GeometricAndMagneticQuantities(BaseModelWithNumpy):
     """Normalization factor used in the threed1 computation."""
 
     b0: float
-    """Magnetic field magnitude on the magnetic axis."""
+    """On-axis R B_phi (``rbtor0``) divided by the major radius of the magnetic axis at
+    phi = 0; the field strength on the axis only for a planar circular axis."""
 
     rmax_surf: float
     """Maximum major radius on the boundary."""