Every other technique in this guide starts from a moment of birth. Horary works on a completely different principle: no birth chart is used at all. Instead, a chart is cast and interpreted for the moment a question is seriously asked and understood by the astrologer, from the place they are in.
The traditional reasoning behind horary is this: if a question genuinely matters, the sky at the moment it is asked also carries information about it. This sits outside the modern scientific frame; it is a wholly traditional (medieval and Hellenistic) astrological discipline — perhaps the oldest and most codified branch of the subject.
Typical questions: "Will I find the thing I lost?", "Should I accept this job offer?", "Will that person call me?" Horary does not try to read the future so much as the present state of the question right now.
Natal, synastry, transit, progression — all of them depend on a moment of birth and require birth data. Horary needs no birth data whatsoever; all it takes is the moment and place the question was asked (or precisely understood by the astrologer). That makes horary the one technique usable even by people whose birth time is unknown or has never been rectified.
A different approach for when the birth time is uncertain.
The chart of the birth moment that every other technique rests on.