diff --git a/lisainstrument/instrument.py b/lisainstrument/instrument.py
index 76d077fa044c96aa80627dee3e8dc3a4e1796f16..f5ae4cde84da6aaa0800890594b2c7684f360fc8 100755
--- a/lisainstrument/instrument.py
+++ b/lisainstrument/instrument.py
@@ -207,7 +207,8 @@ 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 = 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)
@@ -801,12 +802,13 @@ class Instrument:
         self.simulate_noises()
 
         logger.debug("Computing local timer deviations")
+        t = self.physics_et
         self.local_timer_deviations = \
-            self.clock_offsets + \
-            self.clock_freqoffsets * self.physics_t + \
-            self.clock_freqlindrifts * self.physics_t**2 / 2 + \
-            self.clock_freqquaddrifts * self.physics_t**3 / 3 + \
-            ForEachSC(lambda sc:
+            self.clock_offsets \
+            + self.clock_freqoffsets * t \
+            + self.clock_freqlindrifts * t**2 / 2 \
+            + self.clock_freqquaddrifts * t**3 / 3 \
+            + ForEachSC(lambda sc:
                 cumulative_trapezoid(np.broadcast_to(
                     self.clock_noise_fluctuations_withinitial[sc],
                     self.physics_size + self.initial_telemetry_physics_size),
@@ -837,7 +839,7 @@ class Instrument:
             0 if self.tdir_tone_amplitudes[mosa] == 0 \
             else self.tdir_tone_amplitudes[mosa] * np.sin(
                 2 * np.pi * self.tdir_tone_frequencies[mosa]
-                * (self.physics_t + self.local_timer_deviations[mosa[0]])
+                * (self.physics_et + self.local_timer_deviations[mosa[0]])
                 + self.tdir_tone_initial_phases[mosa]
             )
         )
@@ -1333,7 +1335,7 @@ class Instrument:
             self.clock_noise_offsets = self.clock_freqoffsets
         else:
             logger.debug("Generating clock noise offsets")
-            t = self.physics_t
+            t = self.physics_et
             self.clock_noise_offsets = \
                 self.clock_freqoffsets \
                 + self.clock_freqlindrifts * t \
diff --git a/tests/test_instrument.py b/tests/test_instrument.py
index bb97ee9972d855e9c58057c502fcba1c21ec091c..54adb731c58fedd3dcdf3855f0bd5df966c53c42 100755
--- a/tests/test_instrument.py
+++ b/tests/test_instrument.py
@@ -38,13 +38,11 @@ def test_esa_orbits_1_0_2():
     instru = Instrument(size=100, orbits='tests/esa-orbits-1-0-2.h5')
     instru.simulate()
 
-@pytest.mark.skip("see https://gitlab.in2p3.fr/lisa-simulation/instrument/-/issues/83")
 def test_keplerian_orbits_2_0_dev():
     """Test that simulations can run with Keplerian orbit files v2.0.dev."""
     instru = Instrument(size=100, orbits='tests/keplerian-orbits-2-0-dev.h5')
     instru.simulate()
 
-@pytest.mark.skip("see https://gitlab.in2p3.fr/lisa-simulation/instrument/-/issues/83")
 def test_esa_trailing_orbits_2_0_dev():
     """Test that simulations can run with ESA trailing orbit files v2.0.dev."""
     instru = Instrument(size=100, orbits='tests/esa-trailing-orbits-2-0-dev.h5')