64th Navamsa as well as 22nd Drekkana is given utmost importance in dilineating evils on a native. A small note on this issue is presented in this article.
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If the Lagna falls in the first navamsa then the 63rd navamsa would be the last navamsa of the 7th house and the 64th navamsa would be the 1st navamsa of the 8th house. Thus whichever navamsa lagna is in, the same navamsa of the 8th sign from the Lagna becomes the 64th navamsa. However, if you take the equal house system only, then you can say that the navamsa of the cusp of the 8th house falls in the 64th Navamsa.
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In my chart, the lagna is in Sagittarius rasi in the 3rd Navamsa i.e., Gemini. For the sagittarius rasi, the navamsa starts from Aries, since Sagittarius is a dual sign and for all dual signs, the Navamsa starts from the 5th from it. Lagna being in the 3rd Navamsa shall fall in Gemini in the Navamsa Chart.
Now the 8th house from Sagittarius is Cancer and the 3rd Navamsa of Cancer should be Virgo. Hence Virgo becomes the 64th navamsa. In all cases it would fall in the 4th from Navamsa Lagna.
However, as of my knowledge, the 64th Navamsa from Moon is more potent to trouble than that of the Lagna. You can check it out yourself. In my cases, Moon is in Scorpio Navamsa and 4th wherefrom becomes the 64th Navamsa. Thus Aquarius happens to be the 64th navamsa from Moon and Saturn's transit on that sign in the rasi chart was really troublesome.
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Here we are talking on nothing but the Transit on the house cusps (in Rasi) in the divisional chart, whic in this case happens to be the Navamsa. Thus to find out the exact time Saturn Transits over the 64th Navamsa, it is important to know the 8th house cusp, which happens to be the same as the Lagna longitude in equal house system.
The cusps play a very important role in the horoscope analysis and without understanding them the extent on the planetary effect on us is incomplete. It is a known fact that if a planet is near a cusp in a house, the effect of that planet on the house is maximum and if far, the effect is proportionately reduced. This is true with Transits also.
While I talk of the cusp, as per Sanjayji's teaching I am talking of equal house system, where the cusp of all the houses equals that of the Lagna's longitude but falling in their respective houses. Thus for me if the Lagna is in 9d 30m Sagittarius, then the cusp of all houses would have the same longitude. The way you find the placement of different planets in different divisions, you can find the placement of the cusps in different divisions too. To do this count the required division of Lagna, then count as many division of the house under consideration to find the division where the house cusp shall fall.
For example, my Lagna is in 3rd navamsa, the cusp of 2nd house would be 3rd navamsa of Capricorn which is Pisces and that of 3rd house is 3rd from Aquarius, which is Sagittarius and so. The effect of planets in different areas of one's life can be seen from the transit of planets on different cusps of houses in different divisional charts pertaining to the area of life under consideration.
This is an area which does require considerable research to come up with a consistent framework.