diff --git a/caimira/apps/calculator/__init__.py b/caimira/apps/calculator/__init__.py
index 5445e2e2..ea869fec 100644
--- a/caimira/apps/calculator/__init__.py
+++ b/caimira/apps/calculator/__init__.py
@@ -359,14 +359,13 @@ class CO2Data(BaseRequestHandler):
         Returns a list of tuples containing (index, X-axis value) for the detected significant changes.
         """
 
-        times = CO2_data['times']
-        CO2_values = CO2_data['CO2']
+        times: list = CO2_data['times']
+        CO2_values: list = CO2_data['CO2']
 
         if len(times) != len(CO2_values):
             raise ValueError("times and CO2 values must have the same length.")
 
-        # Convert the input lists to numpy arrays for use with the ruptures library
-        times_np = np.array(times)
+        # Convert the input list to a numpy array for use with the ruptures library
         CO2_np = np.array(CO2_values)
 
         # Define the model for change point detection (Radial Basis Function kernel)
@@ -378,7 +377,14 @@ class CO2Data(BaseRequestHandler):
         # Predict change points using the Pelt algorithm with a penalty value of 15
         result = algo.predict(pen=15)
 
-        return [times_np[idx] for idx in result[:-1]]
+        # Find local minima and maxima
+        segments = np.split(np.arange(len(CO2_values)), result)
+        merged_segments = [np.hstack((segments[i], segments[i + 1])) for i in range(len(segments) - 1)]
+        result_set = set()
+        for segment in merged_segments[:-2]:
+            result_set.add(times[CO2_values.index(min(CO2_np[segment]))])
+            result_set.add(times[CO2_values.index(max(CO2_np[segment]))])
+        return list(result_set)
 
     def generate_ventilation_plot(self, CO2_data: dict, transition_times: typing.Optional[list] = None, ventilation_values: typing.Optional[list] = None):
             times = CO2_data['times']
@@ -411,7 +417,9 @@ class CO2Data(BaseRequestHandler):
             return
 
         if endpoint.rstrip('/') == 'plot':
-            self.finish({'CO2_plot': self.generate_ventilation_plot(form.CO2_data, self.find_change_points_with_pelt(form.CO2_data))})
+            transition_times = self.find_change_points_with_pelt(form.CO2_data)
+            self.finish({'CO2_plot': self.generate_ventilation_plot(form.CO2_data, transition_times),
+                        'transition_times': [round(el, 2) for el in transition_times]})
         else:
             executor = loky.get_reusable_executor(
                 max_workers=self.settings['handler_worker_pool_size'],
diff --git a/caimira/apps/calculator/co2_model_generator.py b/caimira/apps/calculator/co2_model_generator.py
index 1a935577..0187535b 100644
--- a/caimira/apps/calculator/co2_model_generator.py
+++ b/caimira/apps/calculator/co2_model_generator.py
@@ -190,7 +190,9 @@ class CO2FormData(model_generator.FormData):
     def ventilation_transition_times(self) -> typing.Tuple[float, ...]:
         # Check what type of ventilation is considered for the fitting
         if self.fitting_ventilation_type == 'fitting_natural_ventilation':
-            return tuple(self.fitting_ventilation_states)
+            vent_states = self.fitting_ventilation_states
+            vent_states.append(self.CO2_data['times'][-1])
+            return tuple(vent_states)
         else:
             return tuple((self.CO2_data['times'][0], self.CO2_data['times'][-1]))            
 
diff --git a/caimira/apps/calculator/static/js/co2_form.js b/caimira/apps/calculator/static/js/co2_form.js
index 01e073f0..ddbbfd36 100644
--- a/caimira/apps/calculator/static/js/co2_form.js
+++ b/caimira/apps/calculator/static/js/co2_form.js
@@ -215,10 +215,10 @@ function validateCO2Form() {
             const max_presence_time = Math.max(elapsed_time_infected, elapsed_time_exposed);
             const max_transition_time = parsedValue[parsedValue.length - 1] * 60;
 
-            if (max_transition_time < max_presence_time) {
+            if (max_transition_time > max_presence_time) {
               insertErrorFor(
                 $("#DIVCO2_fitting_result"),
-                `The last transition time (${parsedValue[parsedValue.length - 1]}) should be after the last presence time (${max_presence_time / 60}).<br />`
+                `The last transition time (${parsedValue[parsedValue.length - 1]}) should be before the last presence time (${max_presence_time / 60}).<br />`
               );
               submit = false;
             }
@@ -297,6 +297,7 @@ function formatCO2DataForm(CO2_data_form) {
   let CO2_mapping = {};
   CO2_data_form.map((el) => {
     let element = $(`[name=${el}]`).first();
+
     // Validate checkboxes
     if (element.prop('type') == "checkbox") {
       CO2_mapping[element.attr('name')] = String(+element.prop('checked'));
@@ -306,7 +307,9 @@ function formatCO2DataForm(CO2_data_form) {
       CO2_mapping[element.attr('name')] = $(
         `[name=${element.attr('name')}]:checked`
       ).first().val();
-    else CO2_mapping[element.attr('name')] = element.val();
+    else {
+      CO2_mapping[element.attr('name')] = element.val();
+    }
   });
   return CO2_mapping;
 }
@@ -320,9 +323,10 @@ function plotCO2Data(url) {
     }).then((response) =>
       response
         .json()
-        .then((json_response) =>
+        .then((json_response) => {
           $("#CO2_data_plot").attr("src", json_response["CO2_plot"])
-        )
+          $("#fitting_ventilation_states").val(`[${json_response["transition_times"]}]`)
+        })
         .then($("#DIVCO2_fitting_to_submit").show())
         .catch((error) => console.log(error))
     );