Integrating the adjustment in the PID example?

[freckletonj]

In the PID example, there's a line (https://github.com/mstksg/auto-examples/blob/master/src/Recursive.hs#L103):

control  <- sumFromD c0 -< adjustment

I get why one would delay a signal in the recursive setting, but I don't think a PID should integrate adjustment in the first place.

Shouldn't it just be:

...        
        let control = kp * err
                       + ki * cumulativeSum
                       + kd * fromMaybe 0 changes
        response <- blackbox   -< control
    id -< response

[freckletonj]

Ah, I read the code before the readme. But I still don't get why sumFromD is the same as system . delay

currResponse <- system . delay c0 -< control