diff --git a/pydynamo/core/plot_system.py b/pydynamo/core/plot_system.py
index 8786ecd6acbafe88b23d0299762aabd74ffd8cb3..253b37111bf8e3c7f8832fd96475888cc80b276e 100644
--- a/pydynamo/core/plot_system.py
+++ b/pydynamo/core/plot_system.py
@@ -3,6 +3,7 @@ from pyvis.network import Network
 import numpy as np
 
 def plot_system(s, v_names=None, rescale=False, com=True, filter_no=None, scales=None, colors=None, title='', linestyle='-'):
+    assert 'time' in dir(s), "Aucune simulation n'a été lancée pour le système !"
     if not v_names:
         v_names = s.get_vars()
     if isinstance(v_names, str):
@@ -53,7 +54,8 @@ def show_pyvis(s, init_val=True, notebook=False, options=None, highlight=None, c
     return Gq
 
 
-def plot_tabhl(s, name):
+def plot_non_linearity(s, name):
+    assert 'time' in dir(s), "No simulation yet! Please run the system."
     x, y, ylabel, xlabel, title = s.get_tabhl_args(name)
     if x is not None and y is not None:
         plt.plot(x, y)
@@ -62,6 +64,7 @@ def plot_tabhl(s, name):
         plt.title(title)
 
 def compare_systems(s1, s2, v_names, scales=None, rescale=False, *args, **kwargs):
+    assert 'time' in dir(s1) and 'time' in dir(s2), "No simulation yet! Please run the system."
     # remove tables
     v_names = [v for v in v_names if not isinstance(getattr(s1,v), list)]
     if not scales and rescale:
diff --git a/pydynamo/core/system.py b/pydynamo/core/system.py
index 2565b5802477ec1ffa8e41e4e29c5c65f2240d70..1db96216775a0838499ae6cdff0c1c1ca58576d9 100644
--- a/pydynamo/core/system.py
+++ b/pydynamo/core/system.py
@@ -124,7 +124,7 @@ class System:
         argop = self.eqs['update'][name]['args']['fun']['tabhl']['val'].strip()
         argop = re.sub('^\(|\)$', '',re.sub('\.[jk]', '', argop)).strip()
         xlabel = argop + ('\n'+ self.get_comment(argname) if argop==argname else '')
-        return x, f(x), ylabel, xlabel, f'tabhl_{name}'
+        return x, f(x), ylabel, xlabel, f"{name} non-linear function"
 
     def iter_all_eqs(self):
         return chain(*self.eqs.values())