Capacity trend calculations rely on the entirety of a resource metric history, and may deviate depending on the interval and number of data points requested by the UI.
Example: A calculation which requests 10 data points from time A to B may not necessarily be a subset of a calculation requesting 11 data points from time A to B + 1. The UI has a limitation on the number of points being drawn, and uses the requested time to get as close to the limit of points for the interval.
Resolution
This is expected behavior in vRealize Operations Manager 6.6.x and below.