The Road to Quality Control

IIISampling Inspection

We sometimes classify the measurement of items (such as products and their components) by the method used. One such method is to measure a single item several times and so obtain a more accurate measurement. For example, we may measure the diameter of a metal rod several times.

Usually a single measurement provides an answer to a question about a quantity such as length, width, and number. We can measure the resistance of a coil with prescribed engineering tolerance with just one measurement. However, as mentioned before, the values will be different if you measure the resistance of a coil twice. This is because there are several factors, such as temperature, humidity, individual differences, etc. that may affect the measurement. If the differences caused by such factors are considered significant, then you have to measure the same coil several times in order to get a more accurate result.

Another method is to measure the characteristics for several items of the same type. In this method, one or several measurements are taken for each of several items of the same type, to determine how much they differ from each other. It means measuring the diameter of several metal rods or measuring the resistance of several coils, for example.

In addition to these two methods of measurement, we are also able to classify the methods used to record the results of measurement. For quantitative measurements, the measured values may be recorded as is. For example, when measuring ...