diff --git a/glidertest/tools.py b/glidertest/tools.py
index 7ee25d7..3b1f7c9 100644
--- a/glidertest/tools.py
+++ b/glidertest/tools.py
@@ -1,5 +1,6 @@
 import numpy as np
 import matplotlib.dates as mdates
+from matplotlib.dates import DateFormatter
 import pandas as pd
 import seaborn as sns
 from scipy import stats