The morning started normally. I placed my microphone into the calibrator cavity, switched it on, and adjusted my measurement system to read 94.0 dB. Standard procedure, performed thousands of times. The calibrator's tone was steady, the level was — well, the level was whatever the calibrator said it was, and the calibrator said 94 dB. That's the whole point of a calibrator.

Except the calibrator's battery was at 15% of its rated voltage. The specification sheet, buried on page 23 of the manual I had never read in its entirety, stated: 'Output level accuracy is guaranteed for battery voltage above 80% nominal. Below this threshold, output level may decrease by up to 0.3 dB per 10% voltage drop.'

My calibrator was outputting approximately 87 dB instead of 94 dB. I had set my measurement system so that 87 dB read as 94 dB. Every subsequent measurement that day was 7 dB too high. The venue I certified as 'compliant at 93 dBA' was actually at 86 dBA — well under the limit. The venue I flagged as 'dangerously loud at 102 dBA' was actually at 95 dBA — still loud, but not the emergency I reported.

Seven decibels might not sound like much until you remember it represents approximately five times the acoustic power. Every number I reported that day was wrong, in a direction that made quiet things seem loud.

The Moral: Check your calibrator's battery before every use. SonaVyx's calibration workflow includes a reference level verification step — but no software can compensate for a calibrator that's lying to you because it's running on fumes.