by Denis Grutze. Paramenters for the scale() function are values specified as decimal percentages. For example, the method call scale(2.0) will increase the dimension of the shape by 200 percent. 

a = 0.0


def setup():
    size(640, 360)
    noStroke()
    rectMode(CENTER)
    frameRate(30)


def draw():
    global a
    background(102)
    a = a + 0.04
    s = cos(a) * 2

    translate(width / 2, height / 2)
    scale(s)
    fill(51)
    rect(0, 0, 50, 50)

    translate(75, 0)
    fill(255)
    scale(s)
    rect(0, 0, 50, 50)