diff --git a/ConstantVelocityAcquisitionPlugin/constant_velocity_acquisition.py b/ConstantVelocityAcquisitionPlugin/constant_velocity_acquisition.py
index 615be15..1284797 100644
--- a/ConstantVelocityAcquisitionPlugin/constant_velocity_acquisition.py
+++ b/ConstantVelocityAcquisitionPlugin/constant_velocity_acquisition.py
@@ -77,7 +77,6 @@ def update_saving_config(self, model):
         model : object
             navigate model
         """
-        # TODO: number of steps
         return {
             "z": model.configuration["experiment"]["ConstantVelocity"][
                 "number_of_frames"
diff --git a/ConstantVelocityAcquisitionPlugin/controller/constant_velocity_acquisition_controller.py b/ConstantVelocityAcquisitionPlugin/controller/constant_velocity_acquisition_controller.py
index ab75680..61025da 100644
--- a/ConstantVelocityAcquisitionPlugin/controller/constant_velocity_acquisition_controller.py
+++ b/ConstantVelocityAcquisitionPlugin/controller/constant_velocity_acquisition_controller.py
@@ -44,7 +44,26 @@ def func(*args):
                     widget_name
                 ] = value
             except (TypeError, ValueError):
-                pass
+                return
+
+            start_position = self.parent_controller.configuration["experiment"][
+                "ConstantVelocity"
+            ]["start_position"]
+            end_position = self.parent_controller.configuration["experiment"][
+                "ConstantVelocity"
+            ]["end_position"]
+            step_size = self.parent_controller.configuration["experiment"][
+                "ConstantVelocity"
+            ]["step_size"]
+            # calculate the estimated number of frames
+            try:
+                frame_number = abs(end_position - start_position) // step_size
+            except:
+                frame_number = 1
+            self.variables["number_of_frames"].set(frame_number)
+            self.parent_controller.configuration["experiment"]["ConstantVelocity"][
+                "number_of_frames"
+            ] = int(frame_number)
 
         return func
 
@@ -59,7 +78,6 @@ def func(*args):
         return func
 
     def update_axis(self, *args):
-        print("*** update axis!")
         self.parent_controller.configuration["experiment"]["ConstantVelocity"][
             "axis"
         ] = self.variables["axis"].get()