Arudha Lagna (AL) is the reflection of the 1st house—the image the native projects to the world. A person with Ascendant in Libra (diplomatic, artistic) but AL in Aries (bold, pioneering) will be perceived as more assertive than their chart's natural tendency suggests.
Strong AL ruler (well-placed, in own sign, exalted, in friendly sign) = public respect, career success, visibility. Weak AL ruler (debilitated, combust, in enemy sign) = perception is undermined; native may be capable but is not recognized.
Upapada Lagna (UL) governs marriage and partnerships. UL sign, its lord's placement, and the state of Darakaraka relative to UL all predict marriage timing and quality. If DK is in the sign of UL's lord, marriage is strongly indicated.
Key principle: Darakaraka ASPECTED (via rashi drishti) by AL ruler = marriage is likely. DK in AL = spouse is a public figure or marriage brings public recognition. DK in 12th from AL = marriage is secret or delayed.
Upapada Nakshatra: The nakshatra of the Upapada Lagna cusp is said to match the native's spouse's nakshatra (classical text: if native is Ashwini, spouse is often Ashwini too). This is empirical; test it on your own charts.
The engine computes AL and UL, their rulers, and interactions with DK. You will synthesize these to predict marriage timing and spousal compatibility.
Arudha Lagna as public image. AL describes reputation, visibility and how the world reads the native. A strong AL with a weak lagna describes someone widely regarded as successful who does not feel so; the reverse describes genuine capability that goes unrecognised. Neither pattern is a contradiction in the chart.
Upapada and marriage. Upapada Lagna, the arudha of the 12th, is read for marriage, the spouse and the spouse's family. Its lord, its occupants and what aspects it by rashi drishti all describe the marriage's character. The 2nd from Upapada is traditionally read for the durability of the union.
Reading UL with Darakaraka. Upapada describes the marriage as an institution and a social fact; Darakaraka describes the partner as a person. Reading them together gives a fuller picture than either alone, and where they disagree sharply, that tension is usually worth reporting rather than resolving.
The restraint required. Classical texts contain severe statements about afflicted Upapada and marital outcomes. These were written in a different social context and are frequently repeated today without that context. State what the chart indicates as a tendency, and do not present any configuration as a sentence.