4.1 Variant
Realization of the variant is schematically visualized by the Fig. 5. During the preparatory
activities it is necessary to create the check sheet for recording the values of the analysed
quality characteristic and the document called Accompanying process sheet. It obviously
consists of a part with the specifications of the process and product, specification of control
chart (type of control chart, sample size, control interval) and a part for records of values of
a quality characteristic including specification of time of data collection and a sign of person
responsible for data recording. In a case of hand-made control charts this check sheet is
represented by so called Control card even containing a part with control charts.
The Accompanying process sheet is a document where it is necessary to record every
intervention into the process (maintenance activities, machine setting), its changes (change
of operator, material batch change) or identified assignable causes including datum and sign
of a responsible employee. This document could be carried out as a separate one but it could
be a part of the control chart mentioned above.
During preparation of the implementation of SPC it is necessary to decide about rules for
assessment of nonstabilities of the process. It is essential to clearly declare and document
that is considered to be a signal of the process nonstability (if only points out of control
limits or some nonrandom patterns, too. In the second case it is necessary to define that
nonrandom patterns will be applied).
Another task which must be realized before implementation of SPC and which is tightly
connected with SPC as a problem-solving instrument, is an assignment of potential
nonstability causes that have an influence on the variability of the analyzed quality
characteristic of product. Very simple method could be applied to such task – Ishikawa
diagram.