diff --git a/plugins/CustomVariables/Archiver.php b/plugins/CustomVariables/Archiver.php
index 39aa9e6bb735e25196c78d24dccb4c6ab03ae321..5c5fcdf8b6c1c6e9ae4018aa94bfdfe716073703 100644
--- a/plugins/CustomVariables/Archiver.php
+++ b/plugins/CustomVariables/Archiver.php
@@ -245,6 +245,19 @@ class Archiver extends \Piwik\Plugin\Archiver
         }
     }
 
+    /**
+     * Delete Visit, Unique Visitor and Users metric from 'page' scope custom variables.
+     *
+     * - Custom variables of 'visit' scope: it is expected that these ones have the "visit" column set.
+     * - Custom variables of 'page' scope: we cannot process "Visits" count for these.
+     *   Why?
+     *     "Actions" column is processed with a SELECT count(*).
+     *     A same visit can set the same custom variable of 'page' scope multiple times.
+     *     We cannot sum the values of count(*) as it would be incorrect.
+     *     The way we could process "Visits" Metric for 'page' scope variable is to issue a count(Distinct *) or so,
+     *     but it is no implemented yet (this would likely be very slow for high traffic sites).
+     *
+     */
     protected function removeVisitsMetricsFromActionsAggregate()
     {
         $dataArray = & $this->dataArray->getDataArray();