Property values by inspection characteristics can be divided into sampling Sampling Inspection and measurement sampling two categories. Counting the piece also includes sampling and sampling point count sampling, sampling is based on the piece in the sample being tested several substandard products, infer whether the entire batch of products received; whereas interest point sampling is based on the sample was seized the product contains the number of unqualified inferred entire batch of products received or not. Sampling inspection is detected by measuring a sample of the product quality and characteristics of the specific values to compare with the standard, and then infer the reception or the entire batch. Press the sampling frequency that is the number of samples (not referring to the number of unit product extracted, ie sample size), sampling can be divided into a sampling, the second sampling, multiple sampling and sequential sampling . A sampling inspection lot is only collected from a sample batch of products made on whether to accept the judgment; secondary sampling is a sampling of the extension, which requires a number of products being drawn up to make a batch of two samples receiving the conclusion whether or not, when the sample can not be determined from a batch or when received, pulls out the second sample, and the results of the two samples to determine whether the batch is received. Subsampling multiple sampling is to further promote, for example, five sampling, allows a maximum of five samples taken before ultimately determine whether to receive approval. Unlimited number of sequential sampling, each taking one unit of product until approved by the rules to make the judgment whether to receive so far.