The calibration certificate was laminated, which should have been the first warning sign. Nobody laminates a document they plan to replace annually. It sat proudly in Gerald's measurement kit, dated June 14, 2019, from a UKAS-accredited laboratory. It certified his sound level meter as compliant with IEC 61672-1 Class 1. In 2019.

Gerald had been submitting noise survey reports citing this certificate for seven years. Every report included the line: 'All measurements were taken using a calibrated Class 1 sound level meter (see calibration certificate).' Technically, the statement was true in 2019. By 2026, it was an exercise in creative interpretation.

IEC 61672-1 recommends periodic calibration — typically annually or biennially depending on the jurisdiction. Seven years is not periodic. Seven years is the interval between Olympic Games in the same city. Gerald's meter had been through three house moves, a flood (the meter survived; Gerald's carpet did not), and roughly two thousand field deployments without a single verification measurement.

When the meter was finally sent for recalibration — prompted by a court case that required proof of instrument accuracy — it came back 4.2 dB out of specification in the A-weighted broadband measurement. Four point two decibels across potentially hundreds of regulatory noise assessments. Gerald's lawyer described this as 'unfortunate.' The judge used a different word.

The Moral: Calibration has an expiry date for a reason. SonaVyx's SPL meter prompts for regular calibration checks — and while no software can force you to maintain your hardware, it can at least remind you that laminating a certificate doesn't extend its validity.