You are right about the Placidus system. I only ever use Placidus. I have to use what stands up to the in-depth scrutiny of rectification work and chart validation. Topcentric and Koch are the only other systems that comes close.Equal is not a house system, but an avoidance of the earth-based geometry that underlies house systems. In other words, quick-n-easy. Same for whole signs.
We have so many house systems because so many mathematically inclined persons have lent their abilities to the concept(s), attempting to find a system that could be contrasted and compared with previous ones. We also have them because some astrologers may have noticed discrepancies or inaccuracies with a system used in persons who they know well and not being satisfied with the current choices decided to come up with a new one.
We also have at least two groups of house systems because of two different ways of dividing up the sky: space-based and time-based. Ultimately space and time as separate things is an illusion, but the time-based systems mentioned above are more accurate.
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Soul Stars Astrology - by the declinations guy
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