History version (wwVersion)

The Historian allows you to overwrite a stored tag value with later versions of the value. The original version of the value is still maintained, so that effectively, multiple versions of the tag value exist at the same point in time.

When retrieving data, you can specify whether to retrieve the originally stored version or the latest version that is available. To do this, set the history version option to "Original" for the original version or "Latest" for the latest available version. If you do not specify the version, the latest version is returned.

To distinguish between a latest value and an original value, the Historian returns a special QualityDetail value of 202 for a latest point with good quality.

This option is relevant in all retrieval modes.