And what did you find with Placidus with intermediate Houses that did not show up with other systems?

It's not as simple as that. Again - you are requesting an answer, which requires an entire book to be written and published. The following may be difficult to grasp, but this is not a manuscript for a book, this a comment in a discussioin forum, so I cannot expand the explanation infinitely.

It's all about chart rectification, and it takes years to master the rectification discipline. Let's say that I have a celbrity chart with 7 events, which have been positively identified in the progressive chart for a specific Kündig cut. It means that now I am sure that I am in possession of the correct Kündig cut. Then with the 8th event, only one house system supports the event.

The event could be the person's death (8th house). With e.g. Koch house system, the 8th cusp is in Aries, meaning that the death is signified with an aspect between an axis (radix MC, radix ASC, primary MC or primary ASC) and (transit, radix or secondary) Pluto (the universal ruler of the 8th house) or the ruler of the 8th house, which with Koch is Mars (radix or secondary) and with Placidus is Neptune (transit, radix or secondary). The orbis is required to be within 26', if there is no triggering aspect, or else within 60', if the aspect is triggered by another planet, whose triggering aspect is within 26'.

Repeat the above test case with other events in other celebrity charts like 20-30 times, and then you can be positively sure that Placidus is the only true house system, and all other house systems are fake.

So, I am 61 years old. I have worked with astrology since I was 18 years old. I have built up this knowledge or skill in a very structured way over the years. It's not easy to pass on the knowledge of e.g. the entire rectification discipline in one single comment.

If astrology had been acknowledged as a scientific discipline, then I could have published my discoveries with chart rectification in a scientific magazines, and then I could have referred to these articles in this comment. But astrology is not acknowledged as a scientific discipline, and my resources are limited. I only publish astrology books, when I have enoough money to do so.

On the other hand, all my astrological activities have had this one goal: To pave the way for scientific acknowledgment of astrology. This journey has moved myself further away from traditional astrologers, making me an alien to them. It's like an antagonistic problem, i.e. a problem, which has no solution. No matter what I do, I run into the wall.

I get it!
Here is an explanation by Anthony Louis in a post in 2016
https://tonylouis.wordpress.com/2016/07 ... g-a-chart/

And the 8 rules for Kundig rectification here.
https://groups.google.com/g/alt.astrology/c/7LVthkMK9eM

Would you recommend the book in English on the Kundig method 'The Precise Astrological Prediction' by Irene Christensen?

I don't know about recommending any specific literature. Instead I recommend you to always to search for the truth and put whatever you find under test.

The special thing about the Kündig rectification method is that once a person has experienced how his or her rectified personal birth chart can lay down that person's life in the symbolic astrological language, then that person is sold. It's almost a religious experience - like the one described in the song "I saw the light" by Hank Williams:

https://www.youtube.com/watch?v=xtolv9kM1qk

In the article, you have provided a link to, Anthony Louis writes: "I have experimented a bit with this method and have not been impressed in the small number of charts I tested it against." So he didn't see the light.

The rest of his article is about the so-called Kündig Sun key, which was actually invented or discovered by Danish astronomer and astrologer Tycho Brahe (1546-1601). It's used in primary directions.

Before Tycho Brahe, astrologers would simply use the equation 1 MC degree moved forwards or backwards = 1 year forward or backward.

But using the Sun key means that you replace the first mentioned equation with this equation: 1 year forward or backward in a person's life = the MC moved forward or backward the same distance as the Sun moved on the day the person was born.

Example: Today is July 9th and the Sun moves ahead with 1 degree 1' and 7". If a child was born today, the primary MC would 60 years later have moved 60 degrees forward without the Sun key, and with the Sun key the primary MC would have moved moved 61 degrees and 7'. There is a huge difference, when it comes to which aspects are activated by then.