When astrologers refer to the cusp of a house, they mean the house's starting point

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Note added at 11 min (2010-10-19 09:26:48 GMT)
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What Is An Astrological House Cusp?
The cusp of a House is the point where it begins. A House ends at the cusp of the following House. In the horoscope chart, the Houses (and the Signs) appear in counter-clockwise order, and Houses are numbered from 1 to 12. The cusp of the First House is always shown at the midpoint on the left side of the chart, similar to where 9 would appear on a clock face. Thus the cusp of the Second House would be where the 8 appears on that clock, the Third House cusp at the 7, and the cusp of the Twelfth House at the 10. The Fourth House cusp is always at the very bottom of the chart, the Tenth House cusp always at the highest point. The cusp of the first Sign (Aries) may begin at any point, because the Houses are fixed and the Signs move in a clockwise direction (but are numbered in a counter-clockwise order).

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Note added at 12 min (2010-10-19 09:27:41 GMT)
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Hrot domu, to je začátek domu.