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The import button can be used at any time but make sure the id's used exist in the system. So in practice this functionality is most suitable for usage within the same system.
Selection of time series (since 2020.02)
Since 2020.02 time series selected via the tree will selected in the same way as if they were selected via the graph or table.
When statistical functions are active be aware that changing the selected time series will affect the time series for which statistics are calculated.