When direct measurement is not feasible, it is important to ensure that a surrogate measurement is appropriate. For example, the measurement of tensile strength of vehicle axle nuts was used as a surrogate for durability. The supplier of steel, in order to achieve greater capability lifted their tensile strength of this steel, but in doing so increased the brittleness. Suddenly many more axle nuts snapped on vehicles. This increased customer complaints and re-work.
Measurements give information about individual items, and also processes.
The process information is often more important because, while individual item information tells us about the past and present, it is process information that tells us about the future. Monitoring of error rates of keypunch staff identified areas for elimination of checking Measurement of processes inevitably leads to thinking about variation. Variation A universal feature of processes is variation. Variation makes decisions more difficult but must be allowed for to reach proper conclusions. In assessing its use of data, an organisation should evaluate how far the inevitable variation in processes is measured and allowed for in planning and managing processes.