what is PRESET in the 40$ robot?

[mohamed]

i dont know what is the 20k preset in the 40$ robot so i dont know what to tell to the saleman when i go to buy it
so if anyone send me a pic of it and the function of it that would be great
i searched google and i found that the preset is a like a variable resistance corrent me if i'm wrong and here is a pic of what i had if this is the preset plz tell me

[frank26080115]

Read!

The resistor whose value is 20K is a potentiometer. A potentiometer (pot or preset) is a resistor whose resistance can be changed. In our project, we will be using 20k presets, that is, we will use presets whose resistance can be changed from 0K to 20K.
When the robot is on white surface the light emitted by the LEDs fall on the LDRs and decreases its resistance. This in turn reduces the voltage at Vout. When the robot is on the black line, the light emitted by the LEDs does not reach the LDRs, hence its resistance increases. This in turn increases the voltage at Vout.
During both the cases it is necessary to adjust the 20K preset in such a way that, when the robot is on white surface, voltage at Vout is <0.8V (so that the voltage at the emitter of the transistor is LOW) and when the sensor is on the black line the voltage is >0.8V (so that the voltage at the emitter of the transistor is HIGH).

[mohamed]

Thanks frank i didnt notice that coz i was reading too fast coz i have waterpolo training to catch my mistake