Date: Calendar Era Year Zero Policy Tool

Description

Convert bounded astronomical year numbering to BCE/CE labels.

Civil calendar arithmetic needs explicit year numbering, leap rules and index origins. A weekday mask or Gregorian component operation does not identify a timezone, working calendar or historical calendar reform.

Convert bounded astronomical year numbering to BCE/CE labels.

When to use this tool

Use Date: Calendar Era Year Zero Policy when checking the stated weekday or Gregorian calendar convention.

How to use the tool and how it works

Enter astronomicalYear. 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.

Convert bounded astronomical year numbering to BCE/CE labels. Require astronomicalYear in [-9999,9999]; positive years map to CE unchanged, otherwise BCE eraYear = 1-year.^[1]

Input field	Meaning and units	Accepted input
astronomicalYear	Astronomical Year	Required. Safe integer.

Output field	Interpretation	Returned shape
result	Returned object; expand its named members below.	Required. Object.
result.era	Era	Calculated result member: string.
result.eraYear	Era Year	Calculated result member: number.

json

{
  "input": {
    "astronomicalYear": 0
  },
  "output": {
    "result": {
      "era": "BCE",
      "eraYear": 1
    }
  }
}

Limitations and assumptions

Astronomical year zero becomes 1 BCE; this does not convert historical calendar dates.
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

Use an appropriate full calendar library and authoritative local rules when business days, historical dates or real scheduling matter.

References

Calculation and input contract: date/calendar-era-year-zero-policy — tool.io

Similar or alternative tools

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