Once you've taken the toaster apart you can get a very good sense of how it operates. Here's the basics of how it works:

There is always power running to the toaster when it is plugged in but the electrical circuit is broken until the handle is pressed down. When the handle is pressed down, two switches are closed, closing the circuit and turning on the power to the toaster.

When the power goes on, an electromagnet in the circuit board is turned on, causing a magnet on the toasters handle to bond to the electromagnet and holding the handle down (and keeping the toaster on) until the circuit is broken.

The circuit is broken when a predetermined amount of power has entered the 555 timer chip in the circuit board - when enough power has entered the chip it sends a signal that causes the electromagnet to lose enough of its magnetic field that the handle is released and the bread pops.

The amount of power that flows to the chip is controlled by a potentiometer which is connected to the circular control knob.

If the maximum toasting setting of seven is used, the potentiometer only allows a small amount of the power to flow into the chip, causing it to take longer to reach the required threshold of power and making the bread spend a longer time in the toaster.

On the other hand, if the cancel setting is used, the potentiometer barely offers any resistance at all, allowing the power threshold in the chip to quickly be reached and as a result, rapidly triggering the popping of the toaster.