The day's stem-branch is exact. Index = (JDN + 49) mod 60, the offset calibrated against known dates: 2000-01-01 = 戊午, 1984-02-01 = 乙丑. Sixty characters turning without a single skip since antiquity.
Gregorian → lunar via a compact month-length table (1900–2049) anchored at 1900-01-31. Verified against eleven known Lunar New Years — 2026's falls on Feb 17, so July 20 reads 六月初七.
The officer = (day-branch − month-branch) mod 12, with 建 on the branch that matches the solar month. From 建 the twelve — 除滿平定執破危成收開閉 — govern what the day is fit for.
A continuous 28-day wheel, (JDN + 11) mod 28. Its luminary still tracks the modern weekday — July 20 is 張月鹿, a Monday and a 吉 mansion, exactly as the old七曜 rule demands.
The suitable-and-avoid lists, the auspicious spirits, and the lucky hours are derived from the 建除 officer and the 黃道黑道 hour-gods through a curated rules table drawn from the通書 tradition. This is a faithful reconstruction of how an almanac reasons — not a transcription of one specific temple edition, which would weigh dozens of competing 神煞. The dates, pillars, mansions and lunar reckoning above are exact; the 宜忌 are principled, not scriptural.