diff --git a/README.md b/README.md
index 9086b3b..2891df6 100644
--- a/README.md
+++ b/README.md
@@ -56,6 +56,7 @@ This voltage divider allows to measure the photo-sensor's resistance and determi
 If you don't want to use this feature, connect PA1 to ground for the highest brightness or Vcc for the lowest brightness.
 
 The blue pill has a 32.768 kHz oscillator for the internal RTC, but don't use the LED next to it as it disturbs the oscillator and the time won't stay right.
+In case the time is lagging because RTC oscillation has been skipped, add a button between Vcc and PB8 and each press will increment the time by one second.
 If the board does not provide a 32.768 kHz oscillator for the internal RTC it is also possible to use an external RTC such as the Maxim DS1307.
 The time is then read over I2C and incremented using the square wave output.
 A working example code is under the `DS1307_4096Hz_timer` tag, but needs to be integrated in the latest code state.