Passage: "Every Tuesday, Aling Nena walks from house to house in her barangay with a notebook and a blood pressure monitor. As a barangay health worker, she does not diagnose illness, but she knows which neighbours have missed check-ups, which babies are due for vaccines, and who needs a reminder to take their medicine. Doctors at the rural health unit say her visits catch problems early. When asked why she continues despite the small allowance, she answers simply: 'Kapag malusog ang kapitbahay, panatag ang buong barangay.'" According to the doctors at the rural health unit, what is the value of her visits?