According to Astrological principles, each planet derives a certain amount of strength when it occupies a particular position.  This amount of strength can be measured by certain units called Rupas. 

There are six kinds of planetary strength taken into account in making an assessment of planets for the purpose of making predictions. 

Sthanabala:  This is the positional strength a planet derives from occupying a particular House in the Horoscope.  A planet gets Sthanabala from being in exaltation, in its own House (Swastha or Swakshetra), in a friendly House and its own Shadvargas. 

Digbala: This is the directional strength some planets get when they are placed in certain Houses in a horoscope.  Jupiter and Mercury get Digbala when they are in the East – the 1st House or the Ascendant. Sun and Mars get Digbala in the North represented by the 10th house.  Saturn gains Digbala in the West or in the 7th House. Venus and Moon get Digbala in the South or in the 4th House.

Chestabala: Sun and Moon get Chestabala or motional strength in the signs or the Rashis of Capricorn, Aquarius, Pisces, Aries, Taurus, and Gemini which constitute the Uttarayana or the Sun’s Northerly course. Mars, Mercury, Jupiter, Venus, and Saturn in retrogression or in conjunction with the Full Moon get Chestabala.  If Jupiter, Venus, Mercury, and Saturn are with Mars they are considered defeated in the Graha Yuddha and thereby get Chestabala. 

Kalabala (Temporal strength):  Moon, Mars and Saturn are powerful during the night.  Sun, Jupiter, and Venus are powerful during the day.  Mercury is powerful both during the day and the night.  Malefics are powerful during the dark half of the Lunar month. Mercury, Sun, Saturn, Moon, Venus, and Mars are powerful at sunrise, noon, evening, first part of the night and the last part of the night, respectively.  Jupiter is always powerful.  Planets in their week day, months and years are powerful.

Drugbala:  This Bala is reckoned from the strength of the aspect of one planet over another planet.

Naisargikabala:  This means the intrinsic permanent strength of planets.  Each planet produces a certain measure of strength permanently irrespective of its position.  Sun, Moon, Venus, Jupiter, Mercury, Mars, and Saturn possess measures of permanent strength in their descending order with Sun commanding the highest measure of strength and Saturn the least.