We're now going to make a pulse stretcher that can generate a pulse with a large or small width, just as we want when a trigger pulse is input.
As you'll see in the schematic, S1 is used to generate a trigger pulse. It is sent to the Schmitt circuit that generates a new pulse determined by R (R5 and the control volume). The width of this new pulse can be changed by turning the control volume.
When you finish assembling turn power on. Then, flip S1, and LED 1 goes out immediately and LED 2 also goes out about a second later.
Now turn the control volume counterclockwise, and again flip S1. What happens now?
It takes a longer time, a few seconds, for LED 2 to goes out this time. Set the control volume in different positions and see how this time lag (which is the pulse width) changes.