Numerological texts give two methods for the Life Path and present them as alternatives without saying what turns on the choice. One reduces the month, the day and the year separately and then adds the three results. The other strings all the digits of the date together and adds them in one pass.
For the final single digit the two methods can never disagree. Digit-sum reduction is equivalent to taking a remainder on division by nine, and remainders survive addition, so the digital root of a sum is always the digital root of the sum of the digital roots. Whichever route is taken, the same figure comes out. This is a theorem, not a convention, and it is the reason the whole apparatus of reduction hangs together at all.
Where the methods genuinely part company is over master numbers. Reducing the components separately can produce an eleven or a twenty-two along the way, from a November birth or a day on the twenty-ninth, and the doctrine says such a number is kept rather than reduced. Adding the whole date in one pass never surfaces those intermediate values, so a chart drawn by the second method may show no master number where a chart drawn by the first shows two.
Since master numbers carry the strongest claims in the system, a reader given a Life Path of eleven by one practitioner and two by another has not caught anyone in an error. The two are using different methods, and the sources this atlas cites for the chart do not agree on which is correct.