Reference for Menachot 172:8
(ויקרא כד, ג) מחוץ לפרכת העדות באהל מועד עדות הוא לכל באי עולם שהשכינה שורה בישראל
What is the testimony? Rab said, It was the western lamp<span class="x" onmousemove="('comment',' I.e., the central lamp (for its wick was turned towards the west) , according to the view that the candlestick was so placed that its branches extended to the north and to the south; or the second lamp counting from the east, assuming that the candlestick was so placed that its branches extended to the east and to the west. V. infra 98b.');"><sup>17</sup></span> [of the candlestick] into which the same quantity of oil was poured as into the others,<span class="x" onmousemove="('comment',' Sc. half a log. the quantity estimated to burn through the longest night.');"><sup>18</sup></span>