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Location4 is typically used to define the scan class which a PI Point belongs to, which would correspond to a number greater than 0 in the interface startup file. UFL PI Points do not update at rates defined by these scan classes, so Location4 is not used and you can set it to any number (including 0). Some of our older UFL documentation states this, but, as you've mentioned, the newer UFL manuals do not mention Location4 much.
Let me know if you have any other questions about this.
Thanks for your help.