This part of ISO 3951 specifies a system of sequential sampling plans (schemes) for lot-by-lot inspection by variables. The schemes are indexed in terms of a preferred series of acceptance quality limit (AQL) values, ranging from 0,01 to 10, which are defined in terms of percent nonconforming items.The schemes of ISO 3951 are intended to induce a supplier through the economic and psychological pressure of lot non-acceptance to maintain a process average at least as good as the specified AQL value, while at the same time providing an upper limit for the risk to the consumer of accepting the occasional poor lot.