Shichen Double-Hour Calculator

Description

Compute branchIndex as floor(((hour+1) modulo 24)/2), and return its start/end hours and midnight-crossing flag.

Gan-Zhi combines a ten-stem sequence with a twelve-branch sequence into a sixty-position traditional cycle. Cycle indexes, calendar dates and local clock labels are distinct inputs; the correct calendar assignment must be established separately.

Compute branchIndex as floor(((hour+1) modulo 24)/2), and return its start/end hours and midnight-crossing flag.

When to use this tool

Use Shichen Double-Hour Calculator when you need an explicit traditional cycle-index mapping or step calculation.

How to use the tool and how it works

Enter hour, minute. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read result. Expand result to inspect the returned fields.

Require hour 0-23 and minute 0-59. Compute branchIndex as floor(((hour+1) modulo 24)/2), and return its start/end hours and midnight-crossing flag.^[1]

The Zi two-hour interval spans 23:00 to 01:00; the supplied clock is used without solar-time correction.^[2]

Input field	Meaning and units	Accepted input
hour	Hour	Required. Safe integer.
minute	Minute	Required. Safe integer.

Output field	Interpretation	Returned shape
result	Object containing the calculated members; expand to inspect the fields below.	Required. Object.
result.branchIndex	Zero-based branch order: Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai.	Calculated result member: number.
result.startHour	Start Hour	Calculated result member: number.
result.endHour	End Hour	Calculated result member: number.
result.crossesMidnight	True for Zi, whose interval begins at 23:00 and ends at 01:00.	Calculated result member: boolean.

json

{
  "input": {
    "hour": 23,
    "minute": 30
  },
  "output": {
    "result": {
      "branchIndex": 0,
      "startHour": 23,
      "endHour": 1,
      "crossesMidnight": true
    }
  }
}

Limitations and assumptions

Minutes are validated but do not change the two-hour bin. Local clock input is literal, without timezone, solar-time, calendar, or daylight-saving conversion.
Outputs are nested inside result. Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.

Alternative or Complementary methods

Consult the intended calendrical convention when deriving labels from dates. Keep local time, day boundaries and solar-term rules explicit rather than treating an index calculator as a calendar or predictive model.

References

Calculation and input contract: ganzhi/shichen-from-clock — tool.io
Heavenly Stems and Earthly Branches — Hong Kong Observatory

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