Pulmonary function measurement by instruments and procedures involves consideration of accuracy of measurement. Measured values differ in various degrees from real values. Both systematic and random error occur. Systematic error can be reduced by proper instrument calibration. Random error arises from three instrument characteristics-drift, nonlinearity, and noise. An instrument's accuracy specification should reflect the sum of error from these three characteristics. Various errors of measurement are acceptable or not acceptable, depending on the physiologic function being evaluated. A deviation from true value of ±2.0% may be acceptable in measurement of inspired oxygen concentration in the clinical setting, but an oxygen analyzer with that degree of error would not be suitable for evaluation of oxygen consumption and respiratory quotient, which calls for accuracy of ±0.1% or better. The careful worker understands and is aware of degrees of accuracy necessary to various pulmonary function measurements.
