I encountered a strange issue today. I wrote a portion of a web application using PI Web API as the data source. The pi point data is a development server tag. I was checking my work to confirm if my results in my web application matched the results in ProcessBook. The AF Attribute is 'Ambient Temperature' in my image below, but the phenomenon is observed in all the attributes of the element, and the various pi points I tested. I refreshed both applications to make sure I was looking at the same time range.
This image shows a significant variance in the value of 'Average' between ProcessBook (62.184), and my installation of PI Web API (57.4388). It is worth noting the Minimum and Maximum matched, but not the Average in each case. Has anyone else encountered this? Is this known issue? Could I have a configuration problem with either program? Also, when I tested this in PI Datalink the average matched PI Web API (61.785 vs 61.784 is close enough).