You can find different planets in different Houses or Bhavas. Some planets may be at the Mid Point of the House or Bhava Madhya. Others may be at the beginning and end. The effects of the different planets, in different points of a House cannot be the same. They vary mathematically. The extent of the effects of the House promised by the planet can be measured by Residential Strength of the planet.  

A planet in the junction of a House, Bhava Sandhi, is null and void, Sandhistho Na Phalaprada. On the contrary a planet in the Mid Point of a House, Bhava Madhya, is very potent.  The influence of a House begins from the Beginning Point of the House, Arambha Sandhi and reaches maximum at Mid Point, Bhava Madhya. The effects of the Bhava falls slowly till it is zero at the End of the House, Virama Sandhi.

What about a planet which is situated at the End of the House and Mid Point of that House ? Here, Residential Strength solves the problem !
In order to ascertain the Residential Strength, discern the Start of the Bhava or House, Poorva Bhaga and End of that House, Uttara Bhaga.
In a planet is in the First Half, Poorva Bhaga, then calculate the distance of the planet from the Start of the Bhava.
Arc of Residential Strength = Longitude of the Planet - Longitude of Start of House, Arambha Sandhi
If a planet is in the Second Half, Uttara Bhaga, calculate the End Point of the House and then subtract the planet's longitude from it.




Arc of Residential Strength = Longitude of End Point of House, Virama Sandhi - Longitude of the Planet
To find the Residential Strength, divide the result by the length of the Start Point or the End Point of House.


For planet in First Half
Residential Strength = Arc of Residential Strength / First Half or Poorva Bhaga
For planet in Second Half
Residential Strength = Arc of Residential Strength / Second Half or Uttara  Bhaga

Residential Strength becomes very important when evaluating a planet. It is another diagnostic tool. This tool can work wonders, when we find, that certain planets do not give full effects, positive and negative.
Other factors like aspects on that house, the strength of the lord of that house also should be considered while evaluating the planet, which gives its effects during its periods of Directional Influence or Dasas and its subperiods. Astrology, indeed, is one of the most difficult sciences !


In my horoscope, the longitude of Mars is 85 degrees. The Start of the 12th Bhava is 74 degrees and End is 104 degrees. The Bhava Madhya Point is 89 degrees and Mars is close to its Bhava Madhya Point and hence powerful in Residential Strength,  just 4 degrees away from the Mid Point of 12th House.
It is true that a Doctor will not treat himself. But then it is human to have a peek at one's own horoscope. In mine, Mars is the Twelfth combines with powerful Sun ( 500 Shashitamsas) and Ketu. He receives the aspect of Kodanda Rahu and associates with exalted Jupiter ( 540 shashtiamsas ) in the Bhava Chart.
Mars Dasa took over in Mar 2012 and I am worried. My Adsense earnings came down. I had less space on Eastro Vedica server and more on Stock Market Astrology server and so I put all my videos on the SMA server. I did not mean to crosslink.  But then it was misunderstood. Anyway I had removed all links to SMA from Eastro Vedica.
Mars, despite being a yogakaraka par excellence, being the lord of 5th and 10th, is in the adverse 12th. Even though he combines with exalted Jupiter and powerful Sun and has good residential strength, still he is in the House of Loss. As a functional benefic, He may not harm me, but indicates Adversity of a high order ! I will have to tide over this crisis ! I am wearing Coral for Him and invoking Him and fasting on Tuesdays !