Applies To:
  • CitectSCADA 2.00 2.01 3.00
Summary:
On the mean mean chart page in the example project, if I keep pressing the 'Scroll trend to real time' button the mean values change. Could you please explain how these mean values are calculated. 

Solution:
In SPC mean is calculated on groups of 5 samples. In real time the SPC system will wait until 5 samples have arrived before it calculates the statistics. It will then update the display. However, when it is scrolled to real time if another sample has arrived then it will use that sample instead of waiting for a group of 5. That is, all the existing points will now use a different group of 5 samples. When the display is updated after the calculations all previous mean values will be changed. 
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