Exact
statement of the particular needs to be satisfied, or essential characteristics that a
customer requires (in a good,
material,
method,
process, service,
system, or work) and which a
vendor must deliver. Specifications are written usually in a manner that enables both parties (and/or an
independent certifier) to
measure the degree of
conformance. They are, however, not the same as
control limits (which allow fluctuations within a range), and conformance to them does not necessarily mean
quality (which is a predictable degree of
dependability and uniformity). Specifications are divided generally into two main categories: (1)
Performance specifications: conform to known
customer requirements such as keeping a room's
temperature within a specified
range.
(2) Technical specifications: express the level of performance of the
individual units, and are subdivided into (a) individual
unit specifications which
state boundaries (parameters) of the unit's performance consisting of a
nominal (desired or mandated)
value and
tolerance (allowable departure from the
nominal value, (b)
acceptable quality level which states
limits that are to be satisfied by most of the units, but a certain percentage of the units is allowed to exceed those limits, and (c)
distribution specifications which
define an acceptable statistical distribution (in terms of
mean deviation and
standard Deviation) for each unit, and are used by a
producer to
monitor its
production processes. See also standard.