With the pendulum, you can go by sequential elimination to determine the possible real date of birth, if this means something to you. If you follow this process, repeat a few times. Then get two-three other person to check it independently.
My late father had his official birthday on 24 January. However, as a child his parents always celebrated it on 23 January. He was born within the wedlock of his parents and in private home (that was 1906). I dowsed the date and also used astrology about it. I concluded he was born on 23 January. We kept celebrating on the 24th though.
