diff --git a/docs/source/chapters/chapter6.rst b/docs/source/chapters/chapter6.rst
index 2157c36..22ad5e9 100644
--- a/docs/source/chapters/chapter6.rst
+++ b/docs/source/chapters/chapter6.rst
@@ -98,11 +98,140 @@ Finally, let us write a *run* method:
             self.update_neighbor_lists()
             self.monte_carlo_displacement()
             self.wrap_in_box()
-            # self.update_log_md_mc(velocity=False) --> we will need to add it too
+
+.. label:: end_MonteCarlo_class
+
+Output
+------
+
+To follow the simulation, let us create a new update function. Add the following
+method to the Outputs class:
+
+.. label:: start_Outputs_class
+
+.. code-block:: python
+
+    def update_log_md_mc(self, velocity=True):
+        """Update the log file during MD or MC simulations"""
+        if self.thermo_period is not None:
+            if (self.step % self.thermo_period == 0) \
+                    | (self.thermo_period == 0):
+                # refresh values
+                if velocity:
+                    self.calculate_temperature()
+                    self.calculate_kinetic_energy()
+                    self.calculate_pressure()
+                # convert the units
+                if velocity:
+                    temperature = self.temperature \
+                        * self.reference_temperature  # K
+                    pressure = self.pressure \
+                        * self.reference_pressure  # Atm
+                    Ekin = self.Ekin*self.reference_energy  # kcal/mol
+                else:
+                    temperature = self.desired_temperature \
+                        * self.reference_temperature  # K
+                    pressure = 0.0
+                    Ekin = 0.0
+                volume = np.prod(self.box_size[:3]) \
+                    *self.reference_distance**3  # A3
+                Epot = self.compute_potential(output="potential") \
+                    * self.reference_energy  # kcal/mol
+                density = self.calculate_density()  # Unitless
+                density *= self.reference_mass \
+                    /self.reference_distance**3  # g/mol/A3
+                Na = cst.Avogadro
+                density *= (cst.centi/cst.angstrom)**3 / Na  # g/cm3
+                if self.step == 0:
+                    characters = '{:<5} {:<5} {:<9} {:<9} {:<9} {:<13} {:<13} {:<13}'
+                    print(characters.format(
+                        '%s' % ("step"),
+                        '%s' % ("N"),
+                        '%s' % ("T (K)"),
+                        '%s' % ("p (atm)"),
+                        '%s' % ("V (A3)"),
+                        '%s' % ("Ep (kcal/mol)"),
+                        '%s' % ("Ek (kcal/mol)"),
+                        '%s' % ("dens (g/cm3)"),
+                        ))
+                characters = '{:<5} {:<5} {:<9} {:<9} {:<9} {:<13} {:<13} {:<13}'
+                print(characters.format(
+                    '%s' % (self.step),
+                    '%s' % (self.total_number_atoms),
+                    '%s' % (f"{temperature:.3}"),
+                    '%s' % (f"{pressure:.3}"),
+                    '%s' % (f"{volume:.3}"),
+                    '%s' % (f"{Epot:.3}"),
+                    '%s' % (f"{Ekin:.3}"),
+                    '%s' % (f"{density:.3}"),
+                    ))
+                for output_value, filename in zip([self.total_number_atoms,
+                                                   Epot,
+                                                   Ekin,
+                                                   pressure,
+                                                   temperature,
+                                                   density,
+                                                   volume],
+                                                  ["atom_number.dat",
+                                                   "Epot.dat",
+                                                   "Ekin.dat",
+                                                   "pressure.dat",
+                                                   "temperature.dat",
+                                                   "density.dat",
+                                                   "volume.dat"]):
+                    self.update_data_file(output_value, filename)
+
+.. label:: end_Outputs_class
+
+As well as
+
+.. label:: start_Outputs_class
+
+.. code-block:: python
+
+    def update_data_file(self, output_value, filename):
+        if self.step == 0:
+            f = open(self.data_folder + filename, "w")
+        else:
+            f = open(self.data_folder + filename, "a")
+        characters = "%d %.3f %s"
+        v = [self.step, output_value]
+        f.write(characters % (v[0], v[1], '\n'))
+        f.close()
+
+.. label:: end_Outputs_class
+
+Let us call *update_log_md_mc* from the run method of the MonteCarlo class.
+Let us add a dump too:
+
+.. label:: start_MonteCarlo_class
+
+.. code-block:: python
+
+    def run(self):
+        (...)
+        for self.step in range(0, self.maximum_steps+1):
+            (...)
+            self.wrap_in_box()
+            self.update_log_md_mc(velocity=False)
             self.update_dump_file(filename="dump.mc.lammpstrj")
 
 .. label:: end_MonteCarlo_class
 
+To output the density, let us add the following method to the *Utilities* class:
+
+.. label:: start_Utilities_class
+
+.. code-block:: python
+
+    def calculate_density(self):
+        """Calculate the mass density."""
+        volume = np.prod(self.box_size[:3])  # Unitless
+        total_mass = np.sum(self.atoms_mass)  # Unitless
+        return total_mass/volume  # Unitless
+
+.. label:: end_Utilities_class
+
 Test the code
 -------------
 
@@ -118,6 +247,7 @@ every 10 steps in the dump files, as well as in the log:
 
     mc = MonteCarlo(maximum_steps=100,
         dumping_period=10,
+        thermo_period=10,
         displace_mc = 0.5,
         number_atoms=[30],
         epsilon=[0.1], # kcal/mol