How to fine tune birth time rectification using Shasthyamsa D60 Vedic Astrology chart ?

If one is not very sure of their birth time Astrologer needs to do birth time rectification for their chart. Intially one ascertain whats the Lagna ( Ascendant ) of the Rasi chart then matching other events of life using other divisional charts one can come very close to exact time but still few minutes accuracy is still not garaunteed . Now finally one needs to see the Shasthyamsa chart for plus minus 1 min of accuracy.

For Shasthyamsa chart the dasa to be used is not Vimshottari its "Moola Dasa". For example the person under consideration is already married and have a child . Then just by seeing whether the D60 chart of the person should run the either Dasa or Bhukti of seven lord or dasa of the occupant of planet in 7th bhava for marriage and Dasa or Bhukti of fifth lord or dasa of the occupant of planet in 5th bhava for child birth . Once the lagna of the D60 chart is fixed one can have the birth chart would be within plus minus 1 minute accuracy. Not only that now one can verify all the events of life using Shasthyamsa D60 chart using Moola Dasa. But unless birth chart is rectified for D60 one should not see D60 like Rasi chart .