diff --git a/source/_dashboards/history-graph.markdown b/source/_dashboards/history-graph.markdown
index b1f6bdf0ef8..3a0e1e8b3b7 100644
--- a/source/_dashboards/history-graph.markdown
+++ b/source/_dashboards/history-graph.markdown
@@ -93,6 +93,12 @@ name:
   type: string
 {% endconfiguration %}
 
+### Long term statistics
+
+Home Assistant saves long-term statistics for a sensor if the entity has a state_class of measurement, total, or total_increasing. For short-term statistics, a snapshot is taken every 5 minutes. For long-term statistics, an hourly aggregate is stored of the short-term statistics. Short-term statistics are automatically purged after a predefined period (default is 10 days). Long-term statistics are never purged.
+
+In the history graph card, if the hours to show variable is set to a figure higher than the purge_keep period, long-term statistics will be used, with short term statistics shown in bold.
+
 ### Examples
 
 ```yaml