• Stephen Biss

Digital v. Mercury

Tip 11: Which do you trust? -#duiSimulator thermometers digital v mercury ?

Why do we have a propensity to assume that a digital display is more accurate, precise, and reliable than an old-fashioned mercury thermometer? Mercury thermometers are NIST traceable but may suffer defects if the mercury separates. Digital display simulators come with a certificate from Guth that limits their reliability to defined standards to one year, subject to proper re-calibration annually. Defined Service (including re-calibration) Intervals are essential to reliability. The digital display on a Guth 2100 reads to 1/10 degree C. The printout of temperature on an Intoxilyzer 8000C Test Record reads to 1/100 degree C. Why should we trust either one of them? They are measurements and every measurement has uncertainty related to the measurement. If the police can't produce evidence of the reliability of their measurements of temperature, through proper calculation of the measurement uncertainty, and proof of traceability of the temperature measuring devices, then the measurement is useless. If police can't articulate the protocol they followed in measuring temperature, the measurement is useless. See Strengthening Forensic Science in the United States at pp. 113, 116, 117

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