Hall effect sensors

Other Hardware General Electronics
22

That are quite smooth readings esp compared to the previous ones. You can smooth these readings even more in the loop() e.g. by only adjusting for 25% of the new rpm value;

loop()
{
  if (newRpm)
  {
    newRpm = false;
    int smoothrpm = (3*smoothrpm + rpm)/4;  // weighted average
    Serial.print(millis());
    Serial.print(", ");
    Serial.print(rpm );
    Serial.print(", ");
    Serial.println(smoothrpm );
  }
}