Description
Compare a supplied chart distance to an explicit reference after unit conversion; no acuity score is inferred.
Vision research uses stimulus angles, chart notations, image scales, viewing distances, coordinate origins, and observation windows. These quantities have different denominators and measurement conventions. A conversion or support share does not independently establish a visual measurement or its clinical interpretation.
Compare a supplied chart distance to an explicit reference after unit conversion; no acuity score is inferred.
When to use this tool
Use Chart Distance Unit Basis Flag when you need this image, stimulus, notation, coordinate, or observation component for supplied research data.
How to use the tool and how it works
- Enter distance, suppliedMetersPerUnit, referenceMeters. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read distanceMeters, referenceRatio. Use the output convention below.
For nonnegative distance and positive suppliedMetersPerUnit and referenceMeters return distanceMeters=distance*factor and referenceRatio=distanceMeters/referenceMeters.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| distance | Distance | Required. Finite number; minimum 0. |
| suppliedMetersPerUnit | Supplied Meters Per Unit | Required. Finite number; strictly above 0. |
| referenceMeters | Reference Meters | Required. Finite number; strictly above 0. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| distanceMeters | Distance Meters | Required. Finite number. |
| referenceRatio | Reference Ratio | Required. Finite number. |
{
"input": {
"distance": 20,
"suppliedMetersPerUnit": 0.3,
"referenceMeters": 6
},
"output": {
"distanceMeters": 6,
"referenceRatio": 1
}
}Limitations and assumptions
- The multiplier is meters per source unit. The reference distance is supplied rather than clinically selected, and the tool does not establish actual viewing distance, chart validity, or visual acuity.
- 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 calibrated acquisition and a documented visual or imaging protocol for complete interpretation. Confirm the reporting notation, viewing geometry, image scale, and support of the underlying observations.
References
Similar or alternative tools
- Ophthalmic Chart Distance Letter Height Factor
Geometric equal-angular-size chart scaling, without asserting clinical equivalence between chart designs.
- Ophthalmology Interpupillary Half Distance Offset
Compare explicit total and monocular distance records, without selecting a spectacle fit or determining patient measurements.