I am modeling a way for clients to read the uptime of a machine from an OPC UA server.

I have modeled the UpTime variable with the Duration DataType. The underlying system can only provide the uptime with a precision in minutes, so I would like to add this precision “meta” information.

The optional property “ValuePrecision” of a DataItemType looks like the proper way of modeling this. However the OPC Spec. 1.04 Part 8 – 5.3.1. DataItemType states:

ValuePrecision can be used for the following DataTypes:
• For Float and Double values it specifies the number of digits after the decimal place.
• For DateTime values it indicates the minimum time difference in nanoseconds. For example, a ValuePrecision of 20 000 000 defines a precision of 20 ms.

So the ValuePrecision of a Duration is undefined.

Duration could be added to the second bullet point (DateTime) which I think is a valid addition: A Duration with the ValuePrecision of 20 000 000 then means a precision of 20 ms.