diff --git a/four_levels_model.py b/four_levels_model.py
index d820079..d4a7af5 100644
--- a/four_levels_model.py
+++ b/four_levels_model.py
@@ -146,7 +146,8 @@ class HeatingGas:
         ''' others parameters to be returned '''
         self.g_0, self.distance, self.wavelength, self.wavelength_intensity, self.energy_intensity, self.energy, self.ISRF, RF_list = rf.radiation_field(self.filename, self.star_radius, self.parsec, self.ISRF, RF_list=False)
         self.gamma = ( self.g_0 * np.sqrt(self.t_gas) ) / self.n_e #ionization parameter
-
+        #in cm3 K^1/2
+        
         ''' Ionization Potential (IP) estimation '''
         a = (self.n_c/468)**(1/3) #molecule diameter, in nm
         self.ip_neutral = 3.9 + one_in_4_pi_eps_0 * ( ( z_0 + (1/2) ) * (ev**2/a) + ( z_0 + 2 ) * (ev**2/a) *(0.03/a) ) * (1/ev)
@@ -390,5 +391,6 @@ class HeatingGas:
         ''' gas heating '''
         self.total_gas_heating = total_injected_power * (self.fc_pah/self.n_c) * 2.7e-4
         #2.7e-4 : elemental abundance of C relative to H (Tielens 2021)  
-                
+        #total gas heating in erg s-1 H-1  
+        
         return self.total_gas_heating, self.heating_efficiency, self.g_0 , self.gamma, self.t_gas, self.n_e, self.n_c
\ No newline at end of file
--
libgit2 0.21.2