The value unit class of the detail information specified
in this conceptual row in the 'xcmHrDevDetailTable'.
Usage: Used to select a textual convention for specifying the
value unit of this device detail.
Usage: The 'xcmHrDevDetail[UnitClass|Class]' objects
are used to specify the value syntax AND the value unit of the
'xcmHrDevDetail[Integer|OID|String]' value objects.