pause = 5
xstep = 50 ystep = 5
startx = 50
starty = 400 + ystep / 2

for (y = 0, y < 300, y = y + ystep) {

    move startx (starty+y)
    press BUTTON1
    for (i = 0, i < 600, i = i + xstep) {
        move (startx+i) (starty+y)
        delay pause
    }
    release BUTTON1
    delay (pause*3)
	
}