float rotAngle = 0;

void lineRotate(float armLength, float speed){
  clearDisplay();
  
  strokeWeight(10);                              // Controls thickness of line
  stroke(color(0, 0, 255));

  fill(0,0,0);
  
  if ((screenWidth - menu.width)/calibrator.magx - t > 2*armLength){
    ellipseMode(CENTER);
    ellipse(convertXCoord(centerX), convertYCoord(centerY), 
       (screenWidth - menu.width)/calibrator.magx - t, (screenWidth - menu.width)/calibrator.magx - t);
    
    t = t + speed;
    
  } else {
    ellipseMode(CENTER);
    ellipse(convertXCoord(centerX), convertYCoord(centerY), 2*armLength, 2*armLength);
    line(convertXCoord(centerX), convertYCoord(centerY), 
       convertXCoord(centerX) + armLength*cos(rotAngle*PI/180), convertYCoord(centerY) + armLength*sin(rotAngle*PI/180));    
       
    rotAngle = rotAngle + speed;
  }
}