The manual does not explain exactly what the machine picks up, just differentiation in pulse, but it notes that it shouldn't be an alarming indication, just to retake it and sit very still while doing so. If the irregular symbol
comes up multiple times during a one week period
while taking your BP several times a day, then it's recommended that you bring it up to your doc. It is though a little disconcerting when the irregular symbol comes up and in actuality I felt/heard no abnormal rhythm.