diff --git a/fishbook/reproclasses.py b/fishbook/reproclasses.py
index 95cfab3..9008604 100644
--- a/fishbook/reproclasses.py
+++ b/fishbook/reproclasses.py
@@ -357,10 +357,17 @@ class BoltzmannFit:
 
     @property
     def x_data(self):
+        """ The x data sorted and unique used for fitting.
+        :return: the x data
+        """
         return self.__x_sorted
 
     @property
     def y_data(self):
+        """
+        the Y data used for fitting, i.e. the average rate in the specified time window sorted by the x data.
+        :return: the average and the standard deviation of the y data
+        """
         return self.__y_avg, self.__y_err
 
     def solve(self, xvalues=None):