A Dasa is an Asterism based progression, quite unique to Vedic Astrology. Every graha or planetary body gets a weighted period on which it acts on a native. Those set periods can be recursively divided in similar weighted manner into sub periods and their sub periods, bringing an event’s occurrence to within a few days. Of course, one can recursively traverse the function to get to sub units of time, but for ease of understanding most ancient texts like this blog, limited it to three grahas only.
Understanding a Dasa period is not easy as many factors influence the period it represents. It’s sub divisions make the challenge exponential and further sub divisions further increase the complexity.
Any Dasa combination of Mars, Jupiter and Saturn overwhelms one half of the natal zodiac. These grahas are the lords of 8th, 9th, 10th sign; lords of 11th, 12th and 1st sign. From Scorpio to Aries is completely under the influence of the three Grahas, in their Dasa rulership. Of course, depending on how the houses are distributed from the ascendant (lagna), the combination of the three Grahas can exert lopsided pressures on one half of the native’s chart. I have witnessed some incredible results during the Dasa-Antara-Pratyantara of the three. If the period lasts 6 months, each month gets a unique (3 x 2) influence. Gain in wealth in one month with extra losses in another month, or loss of wealth followed by a gain; loss of health followed by an incredible recovery and similar yin-yang combinations occur within that short span of time.
A similar combination to the one described comes from Sun, Moon and Mercury dasa period. They involve a third of the native’s chart starting from the 3rd to the 6th sign. If such a region lies between 1st to 4th or 2nd to 5th house, the results could be really good.