diff --git a/frappy_psi/tnmr/sequence_fileformat.py b/frappy_psi/tnmr/sequence_fileformat.py
index ce0005ea..51af2ff9 100644
--- a/frappy_psi/tnmr/sequence_fileformat.py
+++ b/frappy_psi/tnmr/sequence_fileformat.py
@@ -236,7 +236,12 @@ def get_event_header(event_type, vals, tables, table_reg, tuning_number, col_del
             
             dwell_us = acq_time / acq_points
             dwell = f'{dwell_us*1000}n'
-            freq = 1/(dwell_us/1e6) / 2 # put it in Hz. TODO: Figure out why the factor of 2 is necessary...
+            
+            # spectral width (here "sweep") and dwell time are linked by the relation
+            # DT = (2*SW)^(-1)
+            # Therefore, SW = 1/(DT*2)
+            
+            freq = 1/(dwell_us/1e6) / 2 # put it in Hz.
             sweep = f'{freq}Hz'
             filtr = f'{freq}Hz'