If you want to search on net then Type Vimshottari Dasha or Vimshottari Dasha in vedic astrology.The dasha that is being discussed is vimshottari Dasha which is considered most reliable than other Dashas.
http://en.wikipedia.org/wiki/Dasha_(astrology)
What is Dasha ?
Dasha is nothing but the ruling period.In vimshottari Dasha Nine planets are considered in order Sun-moon-mars-rahu-Jup-sat-mer-ketu-venus.
The Dasha of sun or ruling period of sun runs for 6 years.So ruling period is always seen and mostly it is used to see changing time and timing of events.
The Dasha of all Nine planets are major ruling period.Major ruling periods runs for long period of time.
Factor considered to judge the effects of ruling period:
1.Position of ruling period planet in Birth chart
2.The sign in which ruling period planet is placed in birth.
3.The ruling period planet is lord of which house.
4.Ruling period planet is under the influence of which planets.
5.Ruling period planet itself is placed where.
Vedic astrology is so vast that the above list can be increased to number of factors.Above factors are just basic factors which are considered.
Additional factors which some astrologers follow and some don't:
1.position of ruling period planet in nakshtra.(used in Kp astrology)
2.the position of lord of that sign and nakshtra in which ruling period planet is placed.Example Dasha running is of Sun.Sun is placed in cancer in Birth chart.Because sun(running dasha)is placed in a sign of moon, position of moon is also considered.
3.Position of ruling period planet in signs in Several Divisional charts.
Note:In vedic astrology Divisional charts are also mentioned which are often not used because it requires very accurate time.Minor Difference in calculation changes position of planet in Divisional charts.some astrologers smartly use it.Decanates and duads in western astrology are similar to Drekkana and Dwadasma Divisional chart.
