Spectacle Bridge Fit Clearance Term Tool

Description

Audit explicit planar bridge/support dimensions without a fitting recommendation.

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.

Audit explicit planar bridge/support dimensions without a fitting recommendation.

When to use this tool

Use Spectacle Bridge Fit Clearance Term 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 bridgeWidth, supportWidth, padIntrusion, asymmetry. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read totalClearance, leftGap, rightGap. Use the output convention below.

For nonnegative bridgeWidth, supportWidth, and padIntrusion return totalClearance=bridge-support-2*pad, leftGap=(bridge-support)/2-pad-asymmetry, and rightGap=(bridge-support)/2-pad+asymmetry.^[1]

Input field	Meaning and units	Accepted input
bridgeWidth	Bridge Width	Required. Finite number; minimum 0.
supportWidth	Support Width	Required. Finite number; minimum 0.
padIntrusion	Pad Intrusion	Required. Finite number; minimum 0.
asymmetry	Signed side-to-side clearance redistribution in the same length unit.	Required. Finite number.

Output field	Interpretation	Returned shape
totalClearance	Total Clearance	Required. Finite number.
leftGap	Left Gap	Required. Finite number.
rightGap	Right Gap	Required. Finite number.

json

{
  "input": {
    "bridgeWidth": 24,
    "supportWidth": 16,
    "padIntrusion": 1,
    "asymmetry": 0.5
  },
  "output": {
    "totalClearance": 6,
    "leftGap": 2.5,
    "rightGap": 3.5
  }
}

Limitations and assumptions

All lengths need one unit and asymmetry is a signed split adjustment. A positive total can coexist with a negative individual gap; no three-dimensional fit, comfort, tissue pressure, or safe frame adjustment is validated.
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

Calculation and input contract: optometry/spectacle-bridge-fit-clearance-term — tool.io

Similar or alternative tools

Spectacle Frame Effective Diameter Clearance
Residual circular blank clearance after supplied frame effective diameter, planar decentration and radial allowance.
Spectacle Asymmetric Frame Decentration Pair
Explicit planar model decentration and conservative circular-blank budget, without selecting spectacle fitting measurements.