X1.5 It is recommended that, if possible, the type of QC
sample that is regularly tested be representative of the material
routinely analyzed. An ample supply of QC sample material
should be available for the intended period of use, and must be
homogenous and stable under the anticipated storage condi-
tions. See Practice D6299 and MNL 7 for further guidance on
QC and control charting techniques..