Time calculation issues – OPC Unified Architecture

The following issues may come up when calculating Aggregates that include time as part of the calculation.

All Aggregate calculations include the startTime but exclude the endTime. However, it is sometimes necessary to return an Interpolated End Bound as the value for an Interval with a timestamp that is in the Interval. Servers are expected to use the time immediately before endTime where the time resolution of the Server determines the exact value (do not confuse this with hardware or operating system time resolution). For example, if the endTime is 12:01:00, the time resolution is 1 second, then the EffectiveEndTime is 12:00:59. If the Server time resolution is 1 millisecond the EffectiveEndTime is 12:00:59.999.
If time is flowing backwards, Servers are expected to use the time immediately after endTime where the time resolution of the Server determines the exact value.
If there is one data point in the Interval and it falls on the StartTime the time duration used in calculations is one unit of the time resolution of the Server.