The easiest way to define a historical parameter string is to copy it from a TrendWorX64 Viewer:
Open GraphWorX64 to a new display.
Add a TrendWorX64 Viewer.
Open the trend configuration.
Select the pen.
Click on the ellipsis (...) button for Connection.
Select Configure.
Use the Connection Configuration dialog to choose your aggregate and other settings.
Click OK.
Copy the text from the Connection field and paste it into your parameters property in the KPIWorX trend or microchart widget.