I have a PCB for a 555 monostable timer circuit as shown below:

![enter image description here][1]

For the most part, the components are clearly labeled (I think the round circle with a + inside denotes a capacitor, but please correct me if I'm wrong). The only component I can't quite identify is the one called "Preset"... 

It has 3 pins, one on top and two on the bottom. The **top pin** is connected to R1 and eventually connects to the VCC and Reset pins on the 555 timer as well as the positive voltage source. The **bottom left pin** of the so called "Preset" component connects to the Discharge pin of the 555 timer. The bottom right pin of the "preset" component does not seem to connect to anything at all, so it surprises me that it's even there to begin with....


What should this "Preset" component be and what is it's role in the circuit? How does its value affect the behavior of the timer circuit?


 [1]: https://i.sstatic.net/DyJ3M.jpg