Chronology Era Zero Label Tool

Description

Return validLabel when hasYearZero or yearLabel is nonzero.

Calendar coordinates depend on an era, origin, day-start rule, and sometimes an arithmetic rather than observational convention. A supplied coordinate difference does not resolve those choices.

Return validLabel when hasYearZero or yearLabel is nonzero.

When to use this tool

Use Chronology Era Zero Label when you need a documented calendar convention or source-coordinate comparison.

How to use the tool and how it works

Enter yearLabel, hasYearZero. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read validLabel, astronomicalYear. Inspect validLabel before interpreting the associated values.

Return validLabel when hasYearZero or yearLabel is nonzero. Preserve astronomical-style numbering when year zero exists, otherwise add one to negative historical labels.^[1]

Input field	Meaning and units	Accepted input
yearLabel	Year Label	Required. Safe integer.
hasYearZero	Has Year Zero	Required. Boolean.

Output field	Interpretation	Returned shape
validLabel	Valid Label	Required. Boolean.
astronomicalYear	Mapped numeric coordinate; inspect validLabel before interpreting an invalid zero label.	Required. Safe integer.

json

{
  "input": {
    "yearLabel": -1,
    "hasYearZero": false
  },
  "output": {
    "validLabel": true,
    "astronomicalYear": 0
  }
}

Limitations and assumptions

A zero historical label yields validLabel false even though astronomicalYear is still returned; inspect the flag before interpreting it, and no era naming or date conversion is inferred.
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 source calendar and authoritative date information for actual observance, conversion, or historical dating.

References

Calculation and input contract: history/chronology-era-zero-label — tool.io

Similar or alternative tools

Calendar Era Order Sign
Take the sign of secondCoordinate-firstCoordinate and reverse it when increasingIsLater is false.
Regnal Year Era Token
Return suppliedFirstYear+regnalYear-1 and a JSON-array key retaining source, era, and regnal year.