Identifying the "Preset" Component in this 555 Monostable Timer PCB

Question

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

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?

UPDATE

Here is a look at the backside of the PCB. I flipped the image horizontally so that the left side of the image of the back PCB aligns with the left side of the image above. Hopefully, this will help to identify how the circuit is layed out:

Answer 1

Here is the most probable schematics:

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

I expect that the "preset" component is a potentiometer. The terminal on the rounded end will be the wiper (moving contact), while the other two terminals are the ends of the resistance element.

Do you have a schematic diagram and/or parts list for this? That should clearly show what this component is.

Varying the pot will likely vary the time of the monostable.

Answer 3

The resistive connection between the Preset (7th terminal) and the Vdd (or capacitor and ground) , would be defining the time intervals of the vibrator. Therefore, I also think that it is a variable resistance.

What I also suspect is that R1 and this pot are in parallel, so if you want to have a fixed time interval, you can choose a resistance, but if you want to modify it; you can stick to a variable pot. However, you should provide a complete schematic to be sure. For example, where is the other pin of the R1 is connected?