- Slate's Paul Adams investigates the $11,000 coffee machine.
quote-PID-unquote? *snerk*, snerks the engineer.
That's Proportional-Integral-Derivative, and it's a kind of controller. The corrections it makes (to the temperature, in this case) are based on the current error (and are proportional to it), the rate of change of the error (its derivative) and a prediction of how it will evolve in the future (which you get via the integral).
This kind of thing is also known as feedback (actually feed-forward in the case of the integral term), which may sound more familiar to you. It's undergraduate-level engineering, although I confess that I have never heard of it being applied to a coffeepot before. Instrumenting the thing with the necessary temperature sensors is probably the hard part.