diff --git a/owlps-positioner/cfg/owlps-positioner.conf b/owlps-positioner/cfg/owlps-positioner.conf
index d2c21a9..43cd207 100644
--- a/owlps-positioner/cfg/owlps-positioner.conf
+++ b/owlps-positioner/cfg/owlps-positioner.conf
@@ -4,6 +4,16 @@
 
 #flush-output-files = true
 
+# "Replay" mode. With this option enabled, the current time is the
+# emission timestamp of the most recent request; you will want to
+# enable this when reading inputs (requests) off-line to replay
+# scenarios, if time-related options are enabled (e.g.
+# positioning.calibration-requests-timeout).
+# To be useful, this option requires the listener's clocks to be
+# synchronised.
+# The default is to run in "live mode", i.e. with this option disabled.
+#replay = off
+
 [data-input]
 # The options in this section are related to the data that are read
 # when the program starts.
@@ -152,7 +162,7 @@ csv-file = /tmp/owlps-positioner.log
 
 # Maximum age of the calibration requests, in seconds. If greater than
 # zero, the positioning requests older than this timeout will be
-# deleted.
+# deleted. See also the replay option.
 #calibration-requests-timeout = 0
 
 # If you activate the above option and want the calibration requests
diff --git a/owlps-positioner/src/userinterface.cc b/owlps-positioner/src/userinterface.cc
index daed267..d51dd2c 100644
--- a/owlps-positioner/src/userinterface.cc
+++ b/owlps-positioner/src/userinterface.cc
@@ -275,7 +275,7 @@ void UserInterface::fill_positioning_options()
   ("positioning.calibration-requests-timeout",
    po::value<unsigned int>()->default_value(0),
    "Maximum age of a calibration request before to delete it"
-   " (0 = unlimited).")
+   " (0 = unlimited). See also the \"replay\" option.")
   ("positioning.position-calibration-requests",
    po::value<bool>()->default_value(false),
    "When accept-new-calibration-requests is activated, allow the"
@@ -339,6 +339,14 @@ void UserInterface::fill_misc_options()
   ("flush-output-files",
    po::value<bool>()->default_value(true),
    "Flush output text files after each line.")
+  ("replay",
+   po::value<bool>()->default_value(false),
+   "\"Replay\" mode. With this option enabled, the current time is the"
+   " emission timestamp of the most recent request; you will want to"
+   " enable this when reading inputs (requests) off-line to replay"
+   " scenarios, if time-related options are enabled (e.g."
+   " \"positioning.calibration-requests-timeout\"). To be useful, this"
+   " option requires the listener's clocks to be synchronised.")
   ;
 
   file_options->add(options) ;