[972] **"Undertaking equanimity, composed in himself (upekkhamārabbha samāhitatto)":** "Equanimity (upekkhā)" means that equanimity in the fourth jhāna — the equanimity, the being equanimous, the looking on with equanimity, the evenness of mind (citta), the tranquility of mind, the neutrality of mind. "Composed in himself (samāhitatto)" means that which is the mind's steadiness, stability, steadfastness, non-distraction, non-scattering, the state of a mind not drawn away, serenity (samatha), the faculty of concentration (samādhi), the power of concentration, right concentration. "Undertaking equanimity, composed in himself" means: having undertaken equanimity in the fourth jhāna, he is one whose mind is unified, whose mind is undistracted, whose mind is not drawn away — thus, "undertaking equanimity, composed in himself."
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.