diff --git a/docs/source/metric.rst b/docs/source/metric.rst
index c1cec1c..02c1eea 100644
--- a/docs/source/metric.rst
+++ b/docs/source/metric.rst
@@ -222,6 +222,31 @@
         
         ...
 
+    Output file format is tab-separated values, with first row specifying names of the columns.  Refer to the following table for the description of the columns:
+
+    +-----------------+---------------------------------------------------------------------+
+    | Column          | Description                                                         |
+    +=================+=====================================================================+
+    | ``Node``        | node id, global unique                                              |
+    +-----------------+---------------------------------------------------------------------+
+    | ``AppId``       | app id, local unique on the node, not global                        |
+    +-----------------+---------------------------------------------------------------------+
+    | ``SeqNo``       | seq number of the Interest-Data                                     |
+    +-----------------+---------------------------------------------------------------------+
+    | ``Type``        | Type of delay:                                                      |
+    |                 |                                                                     |
+    |                 | - ``LastDelay`` means that ``DelayS`` and ``DelayUS`` represent     |
+    |                 |   delay between last Interest sent and Data packet received         |
+    |                 | - ``FullDelay`` means that ``DelayS`` and ``DelayUS`` represent     |
+    |                 |   delay between first Interest sent and Data packet received        |
+    |                 |   (i.e., includes time of Interest retransmissions)                 |
+    +-----------------+---------------------------------------------------------------------+
+    | ``DelayS``      | delay value, specified in seconds                                   |
+    +-----------------+---------------------------------------------------------------------+
+    | ``DelayUS``     | delay value, specified in microseconds (10^-6)                      |
+    +-----------------+---------------------------------------------------------------------+
+
+
 .. _app delay trace helper example:
 
 Example of application-level trace helper