diff --git a/bbn_m5atomS3_lite_alternator_freq_to_RPM/README.md b/bbn_m5atomS3_lite_alternator_freq_to_RPM/README.md
index 0ebe480..0ef9781 100644
--- a/bbn_m5atomS3_lite_alternator_freq_to_RPM/README.md
+++ b/bbn_m5atomS3_lite_alternator_freq_to_RPM/README.md
@@ -41,7 +41,13 @@ Then the frequency of alternator signal can be up to
 
 5000 * N / 60   Hz
 
+Let's say there are 12 poles on alternator N = 12.
 
+5000 * 12 / 60 = 1000 Hz
+
+1/1000Hz = 0.001 sec = 1 millisecond
+
+So debouncing time of 100 microseconds should be ok.
 
 On esp32 there has to be added some synchronization code on the critical section of interrupts (pulses) counting.