The simplest form of quality control was a sketch of the desired item. If the sketch did not match the item, it was rejected, in a simple Go/no go procedure. However, manufacturers soon found it was difficult and costly to make parts be exactly like their depiction; hence around 1840 tolerance limits were introduced, wherein a design would function if its parts were measured to be within the limits. Quality was thus precisely defined using devices such as plug gauges and ring gauges. However, this did not address the problem of defective items; recycling or disposing of the waste adds to the cost of production, as does trying to reduce the defect rate. Various methods have been proposed to prioritize quality control issues and determine whether to leave them unaddressed or use quality assurance techniques to improve and stabilize production.
the sImplEsT forM oF quaLIty contrOl WAS a sketcH Of tHE desIrEd iteM. iF The skEtcH did not maTch tHe item, it Was rejEcTED, in a SimplE gO/NO go ProCedUre. hoWEver, manUfActUrErS Soon fOuND It was difFicuLt And cosTly To mAke parts be exactlY likE their DePicTiOn; hEnCe ARound 1840 tolERance lImITs Were introDuceD, WhereiN a DEsIGN WoULD fuNcTIoN if its paRts were mEasUreD tO Be witHin thE LImiTs. quAliTy was tHus preCisEly defInED UsiNg deViceS such aS pLug gauGes ANd ring gauGes. hoWEveR, tHIS Did nOt aDdress tHe problem of DefeCtive itEms; recyClInG oR dispoSing oF thE wAsTe aDdS TO the cOSt oF ProdUction, as Does tRyInG To reDUcE the defect rAtE. VaRioUs MEthODs have been propoSeD to pRiOritIzE quaLIty control isSuES and deteRmine whetHER to leave ThEm uNadDResSED oR UsE quality aSSurance tecHnIQuEs TO ImPrOVe and stAbiLize productIoN.