Description
Count supplied chart index steps inclusively; no visual acuity conversion or scoring is assumed.
Optical calculations distinguish lens power in diopters, prism notation, angular axes, geometric distances, and visual-acuity reporting scales. Sign conventions and length units are especially important when a formula combines power with decentration or vertex distance. A supplied model term is separate from a validated visual test or prescription.
Count supplied chart index steps inclusively; no visual acuity conversion or scoring is assumed.
When to use this tool
Use Chart Acuity Step Budget when you need this explicit optical, chart, frame, axis, or reference conversion with compatible supplied units.
How to use the tool and how it works
- Enter firstStep, lastStep, excludedSteps. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read nominalSteps, usableSteps. Use the output convention below.
For nonnegative integer firstStep<=lastStep require every excludedStep to lie inside the interval. Return nominalSteps=last-first+1 and usableSteps=nominalSteps minus the number of distinct exclusions.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| firstStep | First Step | Required. Safe integer; minimum 0. |
| lastStep | Last Step | Required. Safe integer. |
| excludedSteps | Excluded Steps | Required. Array of safe integer; maximum items 256. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| nominalSteps | Nominal Steps | Required. Safe integer. |
| usableSteps | Usable Steps | Required. Safe integer. |
{
"input": {
"firstStep": 2,
"lastStep": 8,
"excludedSteps": [
3,
5,
5
]
},
"output": {
"nominalSteps": 7,
"usableSteps": 5
}
}Limitations and assumptions
- Step indices are supplied inclusive integers and repeated exclusions count once. The budget does not parse a chart, set logMAR spacing, interpret unobserved responses, or establish an acuity score.
- 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 the appropriate complete optical or measurement model when a scalar term is insufficient. Verify power, axis, length, notation, and reference conventions before applying the result within a broader assessment.
References
Similar or alternative tools
- Optometric Acuity Log Scale Step Factor
Apply an explicit logMAR step without selecting a chart scoring convention.
- Visual Stimulus Frame Slack
For nonnegative integer availableFrames and requiredFrames and positive frameRate return slackFrames=available-required and slackSeconds=slackFrames/frameRate.