What is POT in this Magnetometer code?

#define SCLK 7 //the clock to pulse
#define MISO 6
#define MOSI 5
#define SSNOT 4 //when low, the device is enabled
#define DRDY 3 //this islow after a reset, high when data is ready
#define RESET 2 //this needs to be toggled low-high-low before each measurement
#define POT 0


//the most significant bit overflowed an int, so these need to be long
long x = 0;
long y = 0;
long z = 0;
int potValue;
long time;


void setup(){
  Serial.begin(9600);


  pinMode(SSNOT, OUTPUT);
  pinMode(RESET, OUTPUT);
  pinMode(MOSI, OUTPUT);
  pinMode(MISO, INPUT);
  pinMode(DRDY, INPUT);
  pinMode(SCLK, OUTPUT);
  pinMode(POT, OUTPUT);


  //i could just ground this line, but this at least marks it as
  //something that one could change if needed
  digitalWrite(SSNOT, LOW);
}


void loop(){
  if (Serial.available()){
    //take the pot measurement first
    potValue = analogRead(POT);
    time = millis();


    //this reads the x, y, and z axes sequentially
    readaxis(0);
    readaxis(1);
    readaxis(2);


    Serial.print(potValue,DEC);
    Serial.print(44,BYTE);
    //this compares the time at which the pot value was read with the time
    //after the magnetometer measurements were taken and the data sent
    Serial.print(time,DEC);
    Serial.print(44,BYTE);
    Serial.print(millis(),DEC);
    Serial.print(44,BYTE);
    Serial.print(13, BYTE);
  }
}


void send_bit(int _high){


  //this sends the bit on the rising edge of the clock


  digitalWrite(MOSI, _high);
  delay(1);
  digitalWrite(SCLK, HIGH);
  delay(1);
  digitalWrite(SCLK, LOW);
  delay(1);
}


int receive_bit(){


  //this receives the data on the falling edge of the clock


  digitalWrite(SCLK, HIGH);
  delay(1);
  int bit = digitalRead(MISO); 
  delay(1);
  digitalWrite(SCLK, LOW);
  delay(1);
  return bit;
}


int readaxis(int _axis){
  //this function sends eight bits, wait until the data is ready
  //and receives 16 bits


    //pulse the reset
  digitalWrite(RESET, LOW);
  delay(1);
  digitalWrite(RESET, HIGH);
  delay(1);
  digitalWrite(RESET, LOW);
  delay(1);


  //send the command byte


  //this sends data that we are not in debug mode
  //and sets the amount of time to read the magnetic sensors (the ASIC period)
  //as /2048 
  send_bit(LOW);
  send_bit(HIGH);
  send_bit(HIGH);
  send_bit(LOW);
  send_bit(LOW);
  send_bit(LOW);


  //the last two bits select the axis
  if (_axis == 0){ //x axis
    send_bit(LOW);
    send_bit(HIGH);
  }
  else if (_axis == 1){ //y axis
    send_bit(HIGH);
    send_bit(LOW);
  }
  else{ //z axis
    send_bit(HIGH);
    send_bit(HIGH);
  }


  //wait until the drdy line is high
  while (digitalRead(DRDY) == LOW){
    //wait
    //Serial.println("waiting"); 
  }
  //Serial.println("data!");


  long runningtotal = 0;


  //receive the results and tally them up as they come in 


  //the leftmost bit signs the number as positive or negative
  long sign = receive_bit();


  for (int i = 14; i >= 0; i = i - 1){
    long thisbit = receive_bit();
    thisbit = thisbit << i;
    runningtotal = runningtotal | thisbit;
  }


  if (sign == 1){
    runningtotal = runningtotal - 32768; 
  }


  if (_axis == 0){
    x = runningtotal;
    Serial.print(x,DEC);
    Serial.print(44, BYTE);
  }
  else if (_axis == 1){
    y = runningtotal;
    Serial.print(y,DEC);
    Serial.print(44, BYTE);
  }
  else{
    z = runningtotal; 
    Serial.print(z,DEC);
    Serial.print(44, BYTE);
  }
}

My guess is it's a potentiometer somehow connected to analog input 0.

potentiometer = variable resistor. frequently abbreviated "pot".

-j

Do you know if I really need to use this? I am not sure why wire/pin to connect this on my magnetometer device.

potentiometer = variable resistor

Being an Olympic standard pedant, I'd have to say it is more like
"potentiometer = 2 * variable resistor" ;D
A variable resistor is a two terminal device, whereas a potentiometer is a three terminal device, and although you can make a variable resistor from a potentiometer, the reverse may not be true.

@MurtyN: a simple way of finding if you need it is to trace through the sketch.
"potVal" is read from the POT pin, and the value printed.
The variable "potVal" is not referenced again anywhere in the sketch, so, you don't need the potentiometer.

Ok. That's what I figured out and went ahead.

Now, I get the readings from the magnetometer for the x and y coordinates. How do I figure out the strength of the magnetic field at any given point?

Is it vector addition?