In any horoscope a planet having highest degrees, minutes and Seconds in any sign is termed as Chara Aatmkarka.

The Chara Aatmkark planet is different from an Aatmkarka planet. Chara Aatmkarka depends on the degrees minutes and Seconds of planets in any sign so it can be different or same in all the horoscope whereas Aatmkarka planet in all the horoscopes remains the same e.g. the natural Aatmkarka in every Horoscope is Sun. You used the word Atmakaraka in your query which is wrong so instead of that the word Chara Aatmkarka should be used.

The then existing concept of Chara Karka was advocated by Vedic muni Parashara in Brihit Parashara Hora Shaastram and it was further propagated by others experts.

Always remember that like the Tripod of Sun, Moon and Lagna, the Tripod of Char Atmakaraka, Char Amatyakarka and Karkansh Lagna also indicates soul, mind and body respectively. It would be a mistake to ignore the Chara Amatyakarka. Imagine if you ignore the Moon while analyzing a horoscope, how will you make predictions? The planet with the second highest degree, minutes and seconds after Aatmkarka is known as Chara Amatyakarka.

In several cases there may be a possibility when two or more planets are found to have the same degrees then in that case Chara Aatmkarka will be decided on the basis of the planet possessing greater minutes. Let us assume two planets with same degrees are found to be candidates in any horoscope and one planet is to be ascended as Chara Aatmkarka.

See the first possibility below for the case of two planets having the same degrees and seconds but different minutes:

1. Sun: 29⁰ 33’ 55”
2. Mars: 29⁰ 34’ 55”

Just focus on the degrees, minutes and seconds of the planets given above which are eligible to become Chara Atmakarakas. You see that the degrees and seconds of the Sun and Mars are the same, 29 and 55 respectively, but the minutes of Mars are 34, which is more than the Sun's 33 minutes, so Mars will be Chara Atmakaraka.

Let us consider the second possibility given below:

1. Sun: 29⁰ 33’ 58”
2. Mars: 29⁰ 33’ 55”

In this situation degrees of Sun and Mars are exactly 29 and minutes of both are also exactly 33 but seconds of Sun mentioned above are 58 which is more than 55 minutes of Mars mentioned above, hence in such situation Sun will be Chara Atmakaraka.

The possibilities mentioned above rarely occur in any horoscope.

There could also be a third possibility given below:

1. Sun: 29⁰ 33’ 55”
2. Mars: 29⁰ 33’ 55”

According to the third possibility above, the degrees, minutes and seconds of the Sun and Mars are the same. In my vast experience of several decades in this field of Vedic Astrology, I have not seen such a position between two planets in any horoscope. This seems to be almost a fantasy, so the process of choosing Chara Atmakaraka will be discussed again whenever I see this position in a horoscope in the future.

Whenever the Chara Atmakaraka planet is found retrograde in a horoscope, a beginning astrologer faces difficulty in making predictions in the initial stage of his practice.

A person who has retrograde Aatmkarka or retrograde Amatyakarka in his horoscope, makes his own path by going against the prevailing thoughts and methods. His long term decisions work without failure.

There is only one rule to calculate the Chara Atmakaraka in any horoscope whether the Chara Atmakaraka is direct or retrograde. The same also applies to other Chara karaka like Chara Amatyakarka etc. irrespective of their motions.