diff --git a/moonwalk.py b/moonwalk.py
index e9c9366..2866a07 100644
--- a/moonwalk.py
+++ b/moonwalk.py
@@ -35,6 +35,38 @@ class Params:
     object_velocity: float = 40 # pixels/second
     velocity_decay: float = 1 # make system a bit springy
 
+    def add_listener(self, attr: str, callback: callable):
+        """
+        Add a listener for a change, callback gets
+        called with (attribute_name, old_value, new_value)
+        """
+        if not attr in self.get_listeners():
+            self._listeners[attr] = []
+        self._listeners[attr].append(callback)
+    
+    def get_listeners(self) -> dict[str, callable]:
+        if not hasattr(self, "_listeners"):
+            self._listeners = {}
+        return self._listeners
+
+    def __setattr__(self, attr, val):
+        if attr == '_listeners':
+            super().__setattr__(attr, val)
+            return
+    
+        if attr == 'tracker_fps' and val < .1:
+            # limit tracker fps
+            val = .1
+    
+        if attr == 'emitter_speed' and val < .1:
+            # limit tracker fps
+            val = .1
+        
+        old_val = getattr(self, attr)
+        super().__setattr__(attr, val)
+        if attr in self.get_listeners():
+            for listener in self._listeners[attr]:
+                listener(attr, old_val, val)
 
         
 class DetectedObject:
@@ -129,6 +161,7 @@ class Canvas:
         for i, field in enumerate(dataclasses.fields(self.params)):
             self.labels[field.name] = pyglet.text.Label(f"{field.name}: {field.default}", x=20, y=30 + 15*(i+1), color=(255,255,255,255), batch=self.batch_info)
         
+        # TODO: Add a number next to the box using pyglet.graphics.Group()
         self.track_shapes = defaultdict(lambda: pyglet.shapes.Box(0,0,0,0,color=(0,255,0),thickness=2, batch=self.batch_bounding_boxes))
 
         self.tracker = Sort(max_age=5, min_hits=2, iou_threshold=0) #DeepSort(max_age=5)
@@ -136,7 +169,15 @@ class Canvas:
         pyglet.clock.schedule_interval(self.on_track, 1/self.params.tracker_fps)
 
         self.interval_items: list[pyglet.clock._ScheduledIntervalItem] = [i for i in pyglet.clock._default._schedule_interval_items if i.func == self.on_track]
+        self.params.add_listener('tracker_fps', self.on_tracker_fps_change)
         
+    def on_tracker_fps_change(self, field, old_value, new_value):
+        """
+        Param dataclass listener for changes to tracker_fps
+        """
+        for ii in self.interval_items:
+            ii.interval = 1/new_value
+            logger.debug(f"Set tracker interval to {ii.interval}")
 
     def run(self):
 
@@ -162,7 +203,7 @@ class Canvas:
 
 
     def on_key_press(self, symbol, modifiers):
-        if symbol == pyglet.window.key.Q:
+        if symbol == pyglet.window.key.Q or symbol == pyglet.window.key.ESCAPE:
             self.window.close()
             exit()
         
@@ -185,7 +226,11 @@ class Canvas:
                 x <= (self.labels[param_name].x + self.labels[param_name].content_width) and \
                 y >= self.labels[param_name].y and \
                 y <= (self.labels[param_name].y + self.labels[param_name].content_height):
-                    setattr(self.params, param_name, param_value+scroll_y)
+                    if scroll_y < 0:
+                        param_value /= (-scroll_y * 1.25)
+                    else:
+                        param_value *= (scroll_y * 1.25)
+                    setattr(self.params, param_name, param_value)
 
 
     def on_track(self, dt):