One division of the Shodashamsha spans 1 degree 52 minutes 30 seconds, sixteen to a sign and 192 in the zodiac. The ascendant crosses that arc in about seven and a half minutes, which is the point at which a divisional chart stops tolerating a remembered birth time.
That threshold is the honest headline for this chart. A time recorded to the minute from a register supports a D-16 reading. A time given as about half past eight does not, and an astrologer who reads a D-16 ascendant from such a time is reading an arbitrary one of four or five possible divisions.
The starting point for the sixteen-fold count is fixed by the modality of the sign, a rule stated in the classical texts.
The Shodashamsha enters the scheme at the dashavarga of ten and continues into the shodashavarga of sixteen. Its subject is vehicles, comforts and the pleasures that come from possessions, a department the tradition treats as distinct from wealth itself, which belongs to the D-2.