Publisher Summary It is known that the estimation of qualitative or quantitative properties of a batch of matter involves a certain number of error-generating operations. These errors must be controlled and their properties mastered. If not, no confidence intervals can be figured out and the resulting estimates are devoid of any practical meaning. The resolution of any problem of quality estimation, whichever it may be, therefore, consists in designing and implementing an estimation scheme with the purpose of: (1) Completely eliminating certain components of error, (2) practically eliminating other components of error, (3) minimizing and evaluating those components of error that can be neither strictly nor approximately eliminated. For that purpose, it is judged useful to recapitulate, in an exhaustive inventory, all errors, or components of error susceptible of altering the critical content of the material during the various steps of the process that leads from the batch L to be valued to the analytical result that will eventually provide an estimate of the batch L content aL.