Flash Guide Number Calculator

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Audio, Music, Photography & Color

Tranche

tranche-4

Evidence ID

t4-205

Ledger rows

1

No ledger note is attached.

Review findings

The core relationship is correct under the stated unit and ISO assumptions. The spec needs an explicit ISO reference for the input GN—normally ISO 100—and explicit same-unit validation before it can receive PASS. The honest label that manufacturer GN ratings are approximate or optimistic should remain visible.

Formula and scope findings

• The GN=aperture*distance relationship is standard, but the stated formulas omit the ISO adjustment; the implementation must explicitly define whether the entered GN is rated at ISO 100 and calculate GN_effective=GN_input*sqrt(ISO/100).
• The spec does not explicitly state that guide number and distance must use the same unit system, such as both meters or both feet.

Unit assumptions

• Guide number and distance use identical units; GN in meters requires distance in meters, and GN in feet requires distance in feet.
• The entered guide number is assumed to be the manufacturer rating at ISO 100.
• ISO scaling uses GN_effective=GN_ISO100*sqrt(ISO/100).
• Aperture is an f-number and is dimensionless for this calculation.
• ISO is a positive numeric sensitivity value.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

Zero distance produces an undefined aperture and would yield Infinity in unvalidated plain JavaScript arithmetic; negative distance also exposes a sign-convention hazard that can produce a nonsensical negative aperture.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "operation": "aperture",
    "guide_number": 36,
    "guide_number_unit": "m",
    "iso": 100,
    "distance": 6,
    "distance_unit": "m"
  },
  "expected_outputs": {
    "aperture": 6,
    "effective_guide_number": 36
  },
  "working": "ISO factor=sqrt(100/100)=1. Effective GN=36*1=36 m. Aperture=effective GN/distance=36/6=6, so the required aperture is f/6."
}

Related workflows

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json