Font Stretch Percent Width Axis

Audit measured width-axis effects on actual samples, using pooled advances rather than equal mean percentages; wdth percent is declared calibration, not guaranteed uniform glyph scaling.

Description

Width-axis calibration compares text advances under two settings.

Width-axis calibration compares text advances under two settings. Pooled advances answer a different question from averaging sample percentages.^[1]

Enter nonempty aligned positive natural/nonnegative stretched advances, finite declared percentage and nonnegative tolerance. Return percentages, strict-deviation indices and pooled percentage.

When to use Font Stretch Percent Width Axis

Use Font Stretch Percent Width Axis when you need to evaluate the supplied records under the calculation and evidence rules below. No uniform glyph scaling or font wdth-axis behavior is guaranteed.

Prepare measured font or typeset-layout values and the explicit design policy requested. For text or font bytes, use the supported syntax explained below.

How to use Font Stretch Percent Width Axis and understand its results

Prepare measured font or typeset-layout values and the explicit design policy requested. For text or font bytes, use the supported syntax explained below.
Enter measuredNaturalTextAdvances, measuredStretchedTextAdvances, declaredWidthAxisPercent, callerDeviationTolerancePercent using the field table and calculation rules, then run the tool.
Read observedWidthPercentages, offCallerAxisCalibrationIndices, pooledWidthPercentage. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
measuredNaturalTextAdvances	Measured natural text advances	list of number	Required
measuredStretchedTextAdvances	Measured stretched text advances	list of number	Required
declaredWidthAxisPercent	Declared width axis percent	number	Required
callerDeviationTolerancePercent	Caller deviation tolerance percent	number	Required

Enter nonempty aligned positive natural/nonnegative stretched advances, finite declared percentage and nonnegative tolerance. Return percentages, strict-deviation indices and pooled percentage.

sample%=100stretched/natural; pooled%=100sum(stretched)/sum(natural)

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
observedWidthPercentages	Observed width percentages	list of number
offCallerAxisCalibrationIndices	Off caller axis calibration indices	list of number
pooledWidthPercentage	Pooled width percentage	number

json

{
  "input": {
    "measuredNaturalTextAdvances": [
      100,
      50
    ],
    "measuredStretchedTextAdvances": [
      90,
      48
    ],
    "declaredWidthAxisPercent": 90,
    "callerDeviationTolerancePercent": 2
  },
  "output": {
    "observedWidthPercentages": [
      90,
      96
    ],
    "offCallerAxisCalibrationIndices": [
      1
    ],
    "pooledWidthPercentage": 92
  }
}

Limitations and assumptions

No uniform glyph scaling or font wdth-axis behavior is guaranteed.

Numeric inputs, where present, must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Numeric lists are limited to 10,000 entries; string lists to 128 strings of at most 128 characters each. The rules above may impose smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Variable Font wght Axis Value Check: A variable font’s declared weight range and named instances define separate checks. Clamping does not erase the original range violation. For a complementary task, use FOUT Layout-Shift Width Delta Check: Font-swap reflow can displace following blocks. A simple displaced-area ratio differs from browser Cumulative Layout Shift.

References

Font Stretch Percent Width Axis — tool.io

Similar or alternative tools

Variable Font wght Axis Value Check
A variable font’s declared weight range and named instances define separate checks. Clamping does not erase the original range violation.
FOUT Layout-Shift Width Delta Check
Font-swap reflow can displace following blocks. A simple displaced-area ratio differs from browser Cumulative Layout Shift.