Description
For nonnegative allowedOffset return netOffset=frameOffset-supportOffset+flexionOffset, absoluteOffset=abs(netOffset), and margin=allowedOffset-absoluteOffset.
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.
For nonnegative allowedOffset return netOffset=frameOffset-supportOffset+flexionOffset, absoluteOffset=abs(netOffset), and margin=allowedOffset-absoluteOffset.
When to use this tool
Use Spectacle Fitting Cantilever Offset Gap 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 frameOffset, supportOffset, flexionOffset, allowedOffset. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read netOffset, absoluteOffset, margin. Use the output convention below.
For nonnegative allowedOffset return netOffset=frameOffset-supportOffset+flexionOffset, absoluteOffset=abs(netOffset), and margin=allowedOffset-absoluteOffset.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| frameOffset | Frame Offset | Required. Finite number. |
| supportOffset | Support Offset | Required. Finite number. |
| flexionOffset | Flexion Offset | Required. Finite number. |
| allowedOffset | Allowed Offset | Required. Finite number; minimum 0. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| netOffset | Net Offset | Required. Finite number. |
| absoluteOffset | Absolute Offset | Required. Finite number. |
| margin | Signed surplus or deficit under the explicitly supplied rule. | Required. Finite number. |
{
"input": {
"frameOffset": 5,
"supportOffset": 2,
"flexionOffset": 1,
"allowedOffset": 6
},
"output": {
"netOffset": 4,
"absoluteOffset": 4,
"margin": 2
}
}Limitations and assumptions
- All offsets need one length unit and axis. The supplied allowance is not a clinical fit limit; deformation, support mechanics, wearer comfort, and safe adjustment are not modeled.
- 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
- Spectacle Bridge Fit Clearance Term
Audit explicit planar bridge/support dimensions without a fitting recommendation.
- Frame Decentration Reference Gap
Compare supplied bench frame and pupil coordinates in one axis basis.