I've found some weird behavior when trying to find the minimum value over a 3 month period with a 1 month time interval and using a filter expression to exclude values less than 50.
When using the Data Item radio button and referencing the cell of the PI Tag and also referencing the cell for the Filter Expression ('TagName'>50) the result returns values greater and less than the filtered expression. Actually, the results returned are the same if the filter expression is there or not.
Now here is where it gets weird! If I select the Expression radio button and reference the PI Tag with the required single quotes with all the other parameters the same, it returns the expected results.
In my view I've done exactly the same thing yet delivers two different results. Is this expected?