diff --git a/examples/scripts/compare_lithium_ion.py b/examples/scripts/compare_lithium_ion.py
index 5b6c81b05e..f18b6121b0 100644
--- a/examples/scripts/compare_lithium_ion.py
+++ b/examples/scripts/compare_lithium_ion.py
@@ -25,4 +25,10 @@
     sims.append(sim)
 
 # plot
-pybamm.dynamic_plot(sims)
+pybamm.dynamic_plot(
+    sims,
+    [
+        "Average negative particle concentration [mol.m-3]",
+        "Average positive particle concentration [mol.m-3]",
+    ],
+)
diff --git a/examples/scripts/compare_particle_models.py b/examples/scripts/compare_particle_models.py
index d780452004..6c515b685c 100644
--- a/examples/scripts/compare_particle_models.py
+++ b/examples/scripts/compare_particle_models.py
@@ -5,16 +5,16 @@
 
 # load models
 models = [
-    pybamm.lithium_ion.DFN(
+    pybamm.lithium_ion.SPM(
         options={"particle": "Fickian diffusion"}, name="Fickian diffusion"
     ),
-    pybamm.lithium_ion.DFN(
+    pybamm.lithium_ion.SPM(
         options={"particle": "uniform profile"}, name="uniform profile"
     ),
-    pybamm.lithium_ion.DFN(
+    pybamm.lithium_ion.SPM(
         options={"particle": "quadratic profile"}, name="quadratic profile"
     ),
-    pybamm.lithium_ion.DFN(
+    pybamm.lithium_ion.SPM(
         options={"particle": "quartic profile"}, name="quartic profile"
     ),
 ]
diff --git a/pybamm/models/submodels/particle/x_averaged_polynomial_profile.py b/pybamm/models/submodels/particle/x_averaged_polynomial_profile.py
index c6a59246bd..b8cdc94a6a 100644
--- a/pybamm/models/submodels/particle/x_averaged_polynomial_profile.py
+++ b/pybamm/models/submodels/particle/x_averaged_polynomial_profile.py
@@ -245,6 +245,7 @@ def set_rhs(self, variables):
             R = variables[f"X-averaged {domain} particle sizes [m]"]
 
         # eq 15 of Subramanian2005
+        # equivalent to dcdt = -i_cc / (eps * F * L)
         dcdt = -3 * j_xav / param.F / R
 
         if self.size_distribution is False:
diff --git a/pybamm/parameters/parameter_values.py b/pybamm/parameters/parameter_values.py
index 51078d0fc1..3eb09b467f 100644
--- a/pybamm/parameters/parameter_values.py
+++ b/pybamm/parameters/parameter_values.py
@@ -696,6 +696,9 @@ def _process_symbol(self, symbol):
             new_symbol.bounds = tuple([self.process_symbol(b) for b in symbol.bounds])
             return new_symbol
 
+        elif isinstance(symbol, numbers.Number):
+            return pybamm.Scalar(symbol)
+
         else:
             # Backup option: return the object
             return symbol