diff --git a/lisainstrument/instrument.py b/lisainstrument/instrument.py
index 0da71415a98254c4d6c848551de4b352edc94d7a..ac81a294b0597387935331c4092d1e16fbf072b1 100644
--- a/lisainstrument/instrument.py
+++ b/lisainstrument/instrument.py
@@ -12,6 +12,7 @@ import re
 import logging
 import h5py
 import scipy.interpolate
+import scipy.integrate
 import numpy
 import matplotlib.pyplot
 
@@ -603,11 +604,11 @@ class Instrument:
 
         logger.debug("Computing local timer deviations")
         self.local_timer_deviations = \
-            self.clock_offsets + ForEachSC(lambda sc:
-                numpy.cumsum(numpy.broadcast_to(
+            ForEachSC(lambda sc:
+                scipy.integrate.cumulative_trapezoid(numpy.broadcast_to(
                     self.clock_noise_offsets[sc] + self.clock_noise_fluctuations[sc],
-                    self.physics_size)
-                * self.physics_dt)
+                    self.physics_size),
+                dx=self.physics_dt, initial=self.clock_offsets[sc])
             )
 
         self.tdir_tones = ForEachMOSA(lambda mosa: