In the Asset Mangement Basics WG we have the use case to provide operation counters.
For this, we defined a standardized name for a FunctionalGroup containing those. WG feels that it would be more appropriate to define this in the Devices spec.

Current text from Asset Management Spec:
When an asset is operated, several numbers might be of interest when managing the asset, like the hours of operation, hours in standby, etc. Those are often the base to calculate KPIs (key performance indicators) like the OEE (overall equipment efficiency). As this specification is just a base specification for asset management, and the counters are domain specific, this specification does not define any of those counters. It just defines a standardized way to find those counters. Other companion specifications or vendors might define those counters.
In order to provide access to the counters, the concept of a FunctionalGroup as defined in OPC 10000-100 is used. This specification just defines the standardized name “OperationCounters”. Servers might provide the counters using different access paths, but they should provide the OperationCounters FunctionalGroup as well. This FunctionalGroup might be organized into other FunctionalGroups, so Clients shall expect that they need to browse several hops to get to all counters.