#include <Servo.h>

Servo servoMotor;
int servoPin = 9

int n = 0;
int q = 1;
int gapSize = 20;

void setup() {
servoMotor.attach(servoPin);
servoMotor.write(n);  // reset clock
delay(1000);
}

void clockwise() {
n = n + gapSize*q;
}

void counterClockwise() {
q = -1;
n = n - gapSize;
}

void loop() {
clockwise();

delay(1000);

if (n > 180) {
counterClockwise();
}

// read the analog input (value between 0 and 1023)
servoMotor.write(n);
delay(15);
}