diff --git a/README.md b/README.md
index 7b0b247..aba8ef4 100644
--- a/README.md
+++ b/README.md
@@ -39,6 +39,12 @@ Connections LED (cathode) <-> board (all LED anodes are connected to the +3.3V r
 - query; PA6
 - submit; PA7
 
+RTC
+---
+
+The onboard Real Time Clock (RTC) is used to track the uptime a periodically start querying all electricity meter for their measurement value.
+The time interval between the periodic queries is hard coded in `main.c`.
+
 ESP8266
 -------