diff --git a/simulations/lib/TravelSignal.py b/simulations/lib/TravelSignal.py
index 70d2863..bd9f90b 100644
--- a/simulations/lib/TravelSignal.py
+++ b/simulations/lib/TravelSignal.py
@@ -116,7 +116,7 @@ class TravelSignal:
             temporal_time_offset = t_f - t_0
 
         # total offset
-        total_time_offset = spatial_time_offset + temporal_time_offset
+        total_time_offset = temporal_time_offset - spatial_time_offset
         n_offset = (total_time_offset * self.sample_rate )
 
         # periodic signal