The CentiCalendar System

The CentiCalendar is a decimal-based calendar system designed to maintain perfect structural consistency, balanced work-rest cycles, and accurate synchronization with the solar year. Its origin aligns with the French Revolutionary adoption of the metric system, making December 31, 1799 the starting point for our calculations.

1. Core Structure

The calendar divides the year into 36 centiweeks, each consisting of 10 days, totaling 360 days. To account for the discrepancy with the solar year (~365.2425 days), five additional "Extra Days" are added each year, lying outside the centiweek cycle. Every 41 years, a full 10-day centiweek, called the "CentiLeap Week" or "Expansion," is added instead of a single leap day, preserving the alignment with the solar year over long periods.

2. Week Structure

• 1 centiweek = 10 days

• Day names: Primeday, Duoday, Triday, Quadraday, Pentaday, Hexaday, Heptaday, Octaday, Enneaday, Decaday

• Work-rest cycle: 3 work days followed by 2 rest days, repeating twice per centiweek

3. Months

The year contains 12 months of 30 days each (3 centiweeks), named to reflect seasonal changes:

1. Aurora

2. Bloom

3. Verdant

4. Solis

5. Ember

6. Harvest

7. Amber

8. Boreal

9. Frostfall

10. Glacia

11. Noctis

12. Zenith

4. Extra Days

Five special days exist outside the weekly and monthly structure:

• New Dawn

• Growth Day

• Midyear

• Reflection Day

• Year's End

These days serve cultural, societal, and seasonal purposes: festivals, reflection, planning, and community events. They do not disrupt the regular 10-day week rhythm.

5. Leap CentiWeek (Expansion)

Every 41 years, a full 10-day centiweek is added to maintain precise alignment with the solar year. This CentiLeap Week is called "The Expansion" and can be used for special celebrations, long-term resets, or global events. Each day within the Expansion is named sequentially: Expansion I, Expansion II, ..., Expansion X.

The next occurrence is calculated by finding the next centiyear divisible by 41 from the current year.

6. Accuracy Across Long Ranges

The CentiCalendar maintains perfect alignment with the Gregorian solar year:

• Each year’s 360 days + 5 extra days = 365 days

• The fractional remainder (~0.2425 days/year) is compensated by the 10-day Expansion every 41 years

• Leap year rules are preserved in conversions to the Gregorian calendar, ensuring precise mapping even centuries later

This design ensures that over long time scales, seasonal drift is minimized to under 1 day per 700 years.

7. Integration With Gregorian Calendar

For practical use, each CentiCalendar day can be mapped to a corresponding Gregorian date. This mapping allows:

• Historical alignment from December 22, 1799 onwards

• Reference for planning, historical research, and scheduling

• Inclusion of extra days and Expansion weeks in calendar applications

8. Work and Rest Cycle

The repeating 3-work / 2-rest pattern provides a balanced schedule, easily implementable in societal, industrial, and educational contexts. Two such cycles occur within each 10-day centiweek, making labor patterns predictable.

9. Visualization and Calendar Implementation

A fully interactive HTML-based CentiCalendar can display:

• Months with weeks numbered (CentiWeek #)

• All days with work/rest status

• Extra Days displayed in correct position

• Leap CentiWeeks highlighted

• Gregorian equivalent date for each centiday

• Accurate date mapping over centuries

10. Historical Context

The start date of December 22, 1799, coincides with winter solstice and the France’s adoption of the metric system by law. This choice underscores the decimal, rational, and systematic nature of the CentiCalendar, emphasizing consistency, precision, and cultural alignment with revolutionary reforms while alligning with traditional celestial measurements. 

11. Conclusion

The CentiCalendar offers a robust, structured, and culturally grounded calendar system. Its combination of decimal weeks, regular months, extra days for festivals and reflection, and the Leap CentiWeek mechanism ensures precise solar alignment and predictable social and work cycles across centuries.