ND Filter Stop / Exposure Time Calculator implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t4-193

Effect

Computation or source lookup only

Input and validation requirements

The specification admits filter_factor = 0, for which log2(0) and the derived stop count are undefined; the calculator must reject it. ND1000 also produces materially different results depending on whether it is interpreted as exact factor 1000 or the common rounded value of 10 stops.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "baseTimeSeconds": 0.008,
    "stops": 3
  },
  "expected_outputs": {
    "newTimeSeconds": 0.064,
    "humanReadable": "64 ms (approximately 1/15.6 s)"
  },
  "working": "2^3 = 8. 0.008 s × 8 = 0.064 s. 0.064 s × 1000 = 64 ms. Reciprocal shutter speed: 1 ÷ 0.064 = 15.625, so approximately 1/15.6 s."
}

Other records

Sources and evidence

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

• VERIFIED_LEDGER.json
• evidence-tranche4/tranche4-results.json