diff --git a/labsw/__init__.py b/labsw/__init__.py
index cc3d3a9..f0edc35 100644
--- a/labsw/__init__.py
+++ b/labsw/__init__.py
@@ -1 +1 @@
-__version__ = '0.1.5.3'
+__version__ = '0.1.5.4'
diff --git a/labsw/io.py b/labsw/io.py
index 647b1af..baedce4 100644
--- a/labsw/io.py
+++ b/labsw/io.py
@@ -2,6 +2,8 @@ import pandas as pd
 import numpy as np
 import yaml
 
+from scipy.signal import savgol_filter
+
 
 def load_data_RH_logger(filepath, every=1):
     """
@@ -21,6 +23,10 @@ def load_data_RH_logger(filepath, every=1):
     # Crop data
     df = df.reset_index()
     del df['index']
+
+    # Derivative
+    df['dmdt'] = savgol_filter(df['weight'], window_length=10000, polyorder=1, deriv=1)
+
     return df.iloc[::every]