The encoding of a performance metric's dimensionality and scale uses
a
pmUnits
structure; see
pmLookupDesc(3).

Given a performance metric value pointed to by
ival
multiply it by a scale factor and return the value in
oval.
The scaling takes place from the units defined by
iunit
into the units defined by
ounit.
Both input and output units must have the same dimensionality.

The performance metric type for both input and output values is determined by
type,
the value for which
is typically extracted from a
pmDesc
structure, following a call to
pmLookupDesc(3)
for a particular performance metric.

pmConvScale
is most useful when values returned via
pmFetch(3),
(and possibly extracted using
pmExtractValue(3))
need to be normalized
into some canonical scale and units for the purposes of computation.

As a special case, if all components of the dimension are zero, then
this is treated as synonymous with a ``count'' dimension of one,
and so the ``count'' scale components determine the relative scaling.
This accommodates the case where performance metrics are
dimensionless, without special case handling on the part of the caller.