Brihat Parashara Hora Shastra
शुक्रेन्दू समभांशेऽन्ये विषमेऽङ्घ्रिमितं बलम् । केन्द्रादिषुस्थिताः खेटाः पूर्णाऽर्धाऽङ्घ्रिमितं क्रमात् ॥ ५॥
Kendradi Bal. A Grah in a Kon gets full strength, while one in Panaphara Bhava gets half and the one in Apoklima Bhava gets a quarter, as Kendradi Bal.
english translation
zukrendU samabhAMze'nye viSame'GghrimitaM balam । kendrAdiSusthitAH kheTAH pUrNA'rdhA'GghrimitaM kramAt ॥ 5॥
hk transliteration by Sanscript