Two Paths To Accuracy
Every solar calendar must correct for the mismatch between day-cycles and year-cycles. HEKA Calendar offers two approaches: one for coordination, one for astronomical purity.
SYNC vs Pure
SYNC Mode
Aligns with Gregorian leap years
March has 30 days when the Gregorian calendar has a leap year (Feb 29). HEKA Calendar April 1st realigns with Gregorian April 1st every year. Perfect for coordinating with the civil world.
Gregorian year is leap
Realignment:
April 1st, annually
- ✓ Matches civil calendar exactly
- ✓ April 1st always aligned
- ✓ Same accuracy as the civil calendar you already trust
- ✓ Recommended for most users
Pure Mode (TRUE)
Follows pure astronomical precision
Uses the "4-year, except 128th" rule. March has 30 days every 4 years, except every 128th year which has 29.
Year ÷ 4 = whole
EXCEPT year ÷ 128
- ✓ Astronomical precision
- ✓ Mean year: 365.242188 days
- ✓ For purists and long-term
The Difference Over Time
In daily life, you won't notice the difference between SYNC and Pure. Pure mode tracks the tropical year to within 0.0000022 days — about one day of drift every 450,000 years. SYNC mode mirrors the Gregorian leap rule instead: exactly as accurate as the civil calendar the world already runs on (one day per ~3,216 years against the tropical year). Pure's trade-off is that its year start drifts slowly against the civil calendar. For most users, SYNC mode provides the best balance of astronomical accuracy and civil coordination.
Why 365.242188 Days?
Pure mode's leap rule yields exactly 365 + 31/128, matching the tropical year (the time from one vernal equinox to the next).
The Components
The Result
The tropical year is approximately 365.2421897 days (IAU 2000 standard). HEKA Calendar's Pure mode achieves 365.242188 — a difference of only 0.0000022 days per year, roughly one day every 450,000 years.
How Calendars Measure Up
Julian
RomanGregorian
CivilHEKA Calendar
Pure ModeTropical year: 365.2421897 days (IAU 2000 standard)