From 279ad1bee0cf7b1ac8c408a7932062f588c32b5e Mon Sep 17 00:00:00 2001
From: Luke Campagnola <luke.campagnola@gmail.com>
Date: Sun, 18 May 2014 19:14:57 -0400
Subject: [PATCH] Fixed ViewBox error when accessing zoom history before having
 zoomed.

---
 pyqtgraph/graphicsItems/ViewBox/ViewBox.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pyqtgraph/graphicsItems/ViewBox/ViewBox.py b/pyqtgraph/graphicsItems/ViewBox/ViewBox.py
index 3fa079f2..d66f32ad 100644
--- a/pyqtgraph/graphicsItems/ViewBox/ViewBox.py
+++ b/pyqtgraph/graphicsItems/ViewBox/ViewBox.py
@@ -1312,6 +1312,8 @@ class ViewBox(GraphicsWidget):
             ev.ignore()
 
     def scaleHistory(self, d):
+        if len(self.axHistory) == 0:
+            return
         ptr = max(0, min(len(self.axHistory)-1, self.axHistoryPointer+d))
         if ptr != self.axHistoryPointer:
             self.axHistoryPointer = ptr