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Mixing Valve Control: Setpoint, Throttling Range, Integral, Derivative-What Does It All Mean?

I'm at a loss in setting up a Honeywell T775 analog controller for mixing boiler return water.

The literature that came with the controller seems to be more aimed at hot air systems vs boiler hot water. It came with a default of 20*F for throttling range, 400 seconds for integral time, and zero for derivative. It recommended keeping the range wide, emphasizing integral time, not messing with derivative.

Can anybody explain or point me to some literature on this?