From b41f0805846f1ba6c2783a71988a46c9ad6358c3 Mon Sep 17 00:00:00 2001
From: Thomas A Caswell <tcaswell@gmail.com>
Date: Thu, 8 Nov 2018 17:25:40 -0500
Subject: [PATCH] Backport PR #12775: Add note to errorbar function about sign
 of errors

---
 lib/matplotlib/axes/_axes.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index 3dfd5502778b..4e9457320c80 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -2949,6 +2949,8 @@ def errorbar(self, x, y, yerr=None, xerr=None,
                 upper errors.
             - *None*: No errorbar.
 
+            Note that all error arrays should have *positive* values.
+
             See :doc:`/gallery/statistics/errorbar_features`
             for an example on the usage of ``xerr`` and ``yerr``.