The jargon Amsa Tulya Rasi means analysing natal positions of planets over the specific divisional charts.
Say for example professional life.
If I take my Dasamsa Chart having Gemini rising in Rasi and Mars in it. And my Dasamsa chart having scorpio rising.
I would take my gemini placed mars ...from rasi chart and place it in the same sign ... gemini in the 8th house over the Dasamsa chart.
So the result would be for lagna lord mars placed in the 8th house in Dasamsa chart in its own sign.
Success in profession/business/service related to the fields signified by gemini plus 8th house, such as work of businessman/ research person / trouble shooter/ facilitator in the field of real estate development/ electrical and mechanical/ sanitary hardware/ insurance etc. etc.
If the signlord of gemini is weak ...there might be some sort of mis-communication or simialar threats. However Lagna of Dasamsa being Mars itself protection would be assured in spite of all the problems.
All the astrologers do not prefer to use the principle of ATR (Amsa Tulya Rasi) as this principle works well subject to certain limitations.
Whereas in the principle of RTA (Rasi Tulya Amsa) we take the rasi chart as the main chart and place the planets in the same sign on rasi chart as they were placed in the divisional charts.
In the above example say for gemini lagna native the sun is placed in the navamsa of pisces. Then under RTA principle... sun would be placed in the 10th house/sign of pisces of the rasi chart.
So during the period or sub-period of sun if the signlord of pisces jupiter is strong in the chart, the person is sure to get a hike in salary or promotion.
The principle of RTA is simply and easy so popular among many astrologers.
It has been used in more than 500 verses of the Chandra Kala Nadi ( Deva Keralam) for delienation of astrological readings.