1.In vedic astrology there are 3 school of thought regarding the recording of the time of birth of a child.
a. When the child comes out of the mother womb.[this is mostly accepted and in use]
b. When you hear the first cry of the child.[I follow this]
c. The time when the umbilical cord is cut.
Practically each of the above will have a time difference of a couple of minutes,this will naturally give error in recording for
2. The next is the location of the spot of birth on earth.
Normally city longitude and latitude are given in ephemeris and these are used by astrologers,now a days the cities are too
large and so have impact on the preparation of a horoscope.
It is recommended to use a mobile phone to record the exact longitude and latitude of the place of birth,this will minimise the error.
3. The third important factor is the ayanamsa used by different astrologers [presently there are over 2 dozens ayanamsa in use]These differen
ayanamsa makes a lot of difference in casting of the horoscope.
QUESTION: WE DO NOT KNOW WHICH AYANAMSA AN ASTROLOGER FOLLOWS AND WE DO NOT REMEMBER WHICH TIME WAS RECORDED AT BIRTH.
THEN HOW ACCURATE HOROSCOPE CAN BE PREPARED?
The answer to this is very simple,the astrologers go for time rectification,they will ask you various questions and adjust your ascendant and navamsa
chart lagna.Further questioning helps them make corrections for further divisional charts.
So if you are looking for the correct answer to your query from an astrologer you should help him with more and more information so that he is HELPFUL.
This way all errors are taken care of automatically.