#include <Servo.h>

Servo arm;
float pos = 0.0;

void setup() {
  // put your setup code here, to run once:
  arm.attach(2); 
  arm.write(pos);
}

void loop() {
  // put your main code here, to run repeatedly:
  while (pos < 180) {
    pos += 0.5;
    arm.write(pos);
    delay(5);
  }
  while (pos > 0) {
    pos -= 0.5;
    arm.write(pos);
    delay(5);
  }
}