let speed = 2;

​

function setup() {

  createCanvas(400, 400);

   angleMode(DEGREES);

}

​

function draw() {

  background(255);

  //draw the shape of the metronome

  strokeWeight(5);

  fill(255);

  quad(175,100,225,100,275,300,125,300);

  fill(0);

  triangle(180,95,220,95,200,80);

  rect(198,100,5,200);

  quad(275,300,125,300,145,240,255,240);

  rect(140,300,10,10);

  rect(250,300,10,10);

  //draw the leg and make it rotate back and forth

  translate(200,240);

  rotate(angle);

  line(0,0,0,-120); 

  angle = angle+speed;

  if (angle==60){

    speed = speed * -1;

  }

  if (angle==-60){

    speed = speed * -1;

  }  

}