From 62fdc1f4d61d29269b8a468057d75c87f59cb320 Mon Sep 17 00:00:00 2001
From: Henry Schreiner <henry.fredrick.schreiner@cern.ch>
Date: Tue, 16 Mar 2021 19:25:34 -0400
Subject: [PATCH] fix: variances was missing sqrt (#150)

---
 docs/changelog.rst | 3 +++
 src/hist/plot.py   | 7 ++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index c85c5fcf..1d08bece 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -4,6 +4,9 @@ Changelog
 Version 2.2.1
 --------------------
 
+* Fix bug with `plot_pull` missing a sqrt.
+  `#150 <https://github.com/scikit-hep/hist/pull/150>`_
+
 * Fix static typing with ellipses.
   `#145 <https://github.com/scikit-hep/hist/pull/145>`_
 
diff --git a/src/hist/plot.py b/src/hist/plot.py
index ad8045ef..560f3d80 100644
--- a/src/hist/plot.py
+++ b/src/hist/plot.py
@@ -170,7 +170,12 @@ def plot_pull(
 
     # Computation and Fit
     values = self.values()
-    yerr = self.variances()
+    variances = self.variances()
+    if variances is None:
+        raise RuntimeError(
+            "Cannot compute from a variance-less histogram, try a Weight storage"
+        )
+    yerr = np.sqrt(variances)
 
     # Compute fit values: using func as fit model
     popt, pcov = curve_fit(f=func, xdata=self.axes[0].centers, ydata=values)