Press a button in the stimulus panel and the value is pushed away from its set point. Signals are released, effectors act, and the value comes back. The two graphs show that loop running.
The upper graph is the value being regulated; the lower one is how much of each signal is present. Both share the same time axis, so the movement of the value and of the signals line up vertically.
The value overshoots before it settles. Signals take time to take effect, so when the value first reaches the set point the signal is still there. This delay is why regulation in living things always wavers a little.
Two opposing hormones are both present even at rest. The balance shifts by one rising as the other falls. Either one reaches zero only when the value is far off.
In the current-state panel you can block a single hormone. Block insulin and blood glucose no longer comes back down: that is diabetes. Watching regulation work is not enough to see what it is worth; you have to break it.
There are no numbers on the time axis. Real regulation takes very different amounts of time for different hormones, and this board compresses it. The vertical axis, on the other hand, shows real values.