PACE Rule - One of the major rules in medical astrology. PACE stands for Placement, Aspect, conjunction, and Exchange. t shows connectivity between houses and planets placed in them. In trine connectivity, planets are considered connected to each other, and results are made on the basis of the connectivity. favorable and friends planet give good result and vise versa. 

Placement - In medical astrology placement means, the position of the planet in a house in the horoscope. Placement of the planet is very important in Medical astrology if the planet is placed well, it will not give you a disease. If a planet is not placed well then the disease will happen. In the chart given below, Saturn's placement is in the  1st house and Mars's placement is in the 10th house. The planets sitting in the 6th, 8th and 12th house give disease in its dasha and antardasha. If any planet is sitting in the house of its enemy or is sitting with the enemy, then it will give disease in its dasha and antardasha. Placement of planets in the 6th, 8th, and 12th house is not considered good.


Aspect - In astrology, every planet has been given a specific Drishti (Aspect).  Wherever the planet sits in the horoscope, it looks at another house or planet with the same aspect assigned to it, and the result is calculated accordingly. In the chart given below Saturn is placed in 1st house and in astrology, Saturn also has three aspects 3rd, 7th, and 10th. The planets Jupiter, Rahu, and Ketu have 3 aspects, 5th, 7th, and 9th respectively, the Sun, Moon, Mercury, and Venus have only one aspect that is 7th from their placement, and mars has three aspects 4th, 7th, and 8th.


Conjunction - When more than one planet is sitting in any one part of the horoscope, then this state is called Yuti or Conjunction. If there are more than three planets then it is called Panchayat. In medical astrology, more than one planet sits in any house, a few points like whether they are enemy or friends or are they placed in friend's or enemy's house must consider. In the chart given below Saturn and Mars occupy the same house. It is called the conjunction of Saturn and Mars in 1st house.


Exchange - When any two planets are sitting in each other's house or house in a horoscope, then it is called an exchange. When two planets sit in each other's zodiac or house, they give mixed results.  You can also say this by ironing that when you are in someone else's house and the same person is in your house then you will not harm the house at that time. In the given chart below Jupiter owner of the 9th house and Moon the owner of the 4th house, are placed in each other's house, it is called the exchange of houses.