One division of the Khavedamsha spans 45 minutes of arc, three quarters of a degree, forty to a sign and 480 in the zodiac. The ascendant crosses that arc in about three minutes.
Three minutes is inside the noise of nearly every birth time, so the house structure of a D-40 belongs to the small class of readings that require a time recorded to the minute by someone present. Stated the other way round: if the time came from a family memory, the D-40 ascendant is not information and should not be presented as any.
The planets survive the same uncertainty. The Moon crosses 45 minutes of arc in about an hour and twenty minutes, the Sun in about eighteen hours, and every slower body in days or longer. A reading of planetary placements in the D-40 from an approximate time is sound; a reading of its houses is not.
The Khavedamsha belongs only to the shodashavarga of sixteen. Its subject is the auspicious and inauspicious effects a person inherits, and the tradition associates it particularly with the maternal line, which pairs it with the D-45 and its paternal counterpart. Read together the two charts express a view of inheritance as something transmitted along two distinct lines rather than as a single undifferentiated legacy.