When you obtain the PID Tuner, you can download all Arduino software required to control the temperature (and any other variable you might like to control such as pressure) by PID loops. You can then immidiately use the PID Tuner to quickly tune the PID loop(s) and monitor and log data.
We went through the tuning steps and this resulted in optimised PID settings.
Figure 3 shows the temperature during operation. Each time the temperature drops, we brew another espresso.
There are possibilities to improve temperature performance, by adding feedforward, but this would require some additional hardware and wiring. If you are interested though, please leave a comment, with your contact details.