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Interpolated data in PI

Question asked by Nandhini8588 on Jun 13, 2019
Latest reply on Jun 26, 2019 by skwan

Hello All,

I need some help with understanding interpolated data in PI. We have a calculation that computes difference of tag values at 8AM current day and 8AM previous day. The tag does not have value at 8AM exactly, and hence the value is interpolated. The calculation is performed using Analytics and scheduled at 8:15AM daily.


TagVal ('Attribute','T+8h') - TagVal ('Attribute','Y+8h')


The calculated results are stored in the Pi Point and the values are slightly different from the one in preview results window. Screenshot as below.

The left one is from Preview Results option in Analytics, while the right one is the archive values of the PI tag updated by analysis.



Is this difference occuring because of difference in interpolated data for the tag? As in, the calculation was scheduled at 8:15 AM, while the preview results are based on interpolated data where there could have been new recorded values now?