diff --git a/lisainstrument/instrument.py b/lisainstrument/instrument.py
index 14afa332770472dad9317c951b181301c294369f..672d04bd531c336633661b3868384f343f3b5444 100755
--- a/lisainstrument/instrument.py
+++ b/lisainstrument/instrument.py
@@ -226,8 +226,8 @@ class Instrument:
         self.physics_dt = self.dt / self.physics_upsampling
         self.physics_fs = self.fs * self.physics_upsampling
         logger.info("Computing physics time vector (size=%s, dt=%s)", self.physics_size, self.physics_dt)
-        self.physics_t = self.t0 + np.arange(self.physics_size, dtype=np.float64) * self.physics_dt
-        self.physics_et = self.physics_t - self.t0 # elapsed time
+        self.physics_et = np.arange(self.physics_size, dtype=np.float64) * self.physics_dt # elapsed time
+        self.physics_t = self.t0 + self.physics_et
 
         # Telemetry sampling
         self.telemetry_downsampling = int(telemetry_downsampling)
@@ -244,9 +244,9 @@ class Instrument:
         logger.info("Computing telemetry time vector (size=%s, dt=%s)", self.telemetry_size, self.telemetry_dt)
         self.telemetry_t = self.telemetry_t0 + np.arange(self.telemetry_size, dtype=np.float64) * self.telemetry_dt
 
-        self.physics_t_withinitial = self.telemetry_t0 + \
+        self.physics_et_withinitial = self.telemetry_t0 - self.t0 + \
             np.arange(self.physics_size + self.initial_telemetry_physics_size, dtype=np.float64) * self.physics_dt
-        self.physics_et_withinitial = self.physics_t_withinitial - self.t0
+        self.physics_t_withinitial = self.t0 + self.physics_et_withinitial
 
         # Orbits, gravitational waves, glitches
         self.init_orbits(orbits, orbit_dataset)