Brihat Parashara Hora Shastra
मध्यमस्फुटयोगार्धहीनं स्वस्वचलोच्चकम् । षड्भाधिकं च्युतं चक्राच्चेष्टाकेन्द्रं स्मृतं कुजात् ॥ २४॥
Motional Strength for Mangal etc. Add together the mean and true longitudes of a Grah and divide the one by two. Reduce this sum from the Seeghroch (or apogee) of the Grah. The resultant product will indicate the Chesht Kendra (or Seeghr Kendra) of the Grah from 12 Rāśis.
english translation
madhyamasphuTayogArdhahInaM svasvacaloccakam । SaDbhAdhikaM cyutaM cakrAcceSTAkendraM smRtaM kujAt ॥ 24॥
hk transliteration by Sanscript