Prior to the early 1990s, attempts were made to quantify odour using dynamic olfactometry. However, the methods available at that time for estimating odour concentrations were generally regarded as being too subjective. Since then, the introduction of improved instrument calibration, the adoption of n-butanol as a reference material, and improved panel screening procedures have made it possible to measure odour concentration objectively.
Precision describes how close repeated measurements are to each other.
An interlaboratory comparison study of olfactometry in Europe was undertaken in 1996. To assess compliance with the overall sensory quality requirements of the standard a reference value of one odour unit corresponding to 123 mg n-butanol evaporated in one cubic metre of neutral gas has been set.