diff --git a/cpdctrl/led_script.py b/cpdctrl/led_script.py
index ffce452..4ae2827 100644
--- a/cpdctrl/led_script.py
+++ b/cpdctrl/led_script.py
@@ -10,6 +10,7 @@ import re
 import numpy as np
 from watchdog.observers import Observer
 from watchdog.events import FileSystemEventHandler
+from typing import Callable
 
 
 class InvalidScript(Exception):
@@ -32,7 +33,7 @@ class LedScriptUpdateHandler(FileSystemEventHandler):
         filename = os.path.basename(self.led_script.filepath)
         if os.path.basename(event.src_path) == filename:
             try:
-                self.led_script.update()
+                self.led_script.update_from_file()
             except ValueError as e:
                 print(e)
 
@@ -42,7 +43,7 @@ class LedScript:
     Class representing a script to control the state of a LED
     """
     ARRAY_DTYPE = [("dt", "f8"), ("dtsum", "f8"), ("led", "i4"), ("line", "i4")]
-    def __init__(self, script:np.ndarray|str|int=0, auto_update=False, verbose=False):
+    def __init__(self, script:np.ndarray|str|int=0, auto_update=False, on_update_callback:Callable[[], None]|None=None, verbose=False):
         """
         Parameters
         ----------
@@ -65,7 +66,7 @@ class LedScript:
 
         """
         self.verbose = verbose
-        self.t_start = 0   
+        self.t_start = None
         self.auto_update = False
         self.filepath = None
         if type(script) == int:  
@@ -83,10 +84,26 @@ class LedScript:
            self.start_updating() 
         self.current_dt = 0
         assert(self.script.shape[0] > 0)
+        self.on_update_callback = on_update_callback
         
     def __del__(self):
         self.stop_updating()
-     
+
+    def reset(self):
+        self.current_dt = 0
+        self.t_start = None
+
+    def copy(self):
+        """
+        Copy-construct a LedScript, always without auto-updates
+        Returns
+        -------
+            New LedScript instance with the same script and same start time
+        """
+        script =  LedScript(self.script.copy(), auto_update=False)
+        script.t_start = self.t_start
+        script.current_dt = self.current_dt
+        return script
         
     def start(self) -> int:
         """
@@ -98,7 +115,7 @@ class LedScript:
             LED Intensity [0,100]
         """
         self.t_start = time.time()
-        return 0
+        return self.get_relative_state(0)
 
     def is_done(self, t: None|float=None) -> bool:
         """
@@ -115,6 +132,7 @@ class LedScript:
         return dt >= self.script["dtsum"][-1]
 
     def get_dt(self, t: None|float=None) -> float:
+        if self.t_start is None: raise RuntimeError("Script must be started before get_dt can be used")
         if t is None: t = time.time()
         return t - self.t_start
         
@@ -223,8 +241,8 @@ class LedScript:
             self.observer = None
             if self.verbose: print("Led script stopped watching for updates")
    
-    def update(self, verbose=True):
-        print(f"Updating led script from '{self.filepath}'")
+    def update_from_file(self, verbose=True):
+        if verbose: print(f"Updating led script from '{self.filepath}'")
         newscript = LedScript.parse_script(self.filepath, ignore_errors=False)
         idx = self.get_current_index(self.current_dt)
         # check that all past command dts are the same
@@ -237,6 +255,7 @@ class LedScript:
         if idx != newidx:
             raise ValueError(f"The duration of the current step {idx+1} in line {newscript['line'][idx]} in the new script is too short TODO") 
         self.script = newscript
+        if self.on_update_callback is not None: self.on_update_callback()
     
     @staticmethod
     def parse_script(filepath: str, ignore_errors:bool=False) -> np.ndarray|tuple[np.ndarray, list[InvalidScript]]: