Once the Atmos clock has been levelled and the hands set, the locking mechanism can be undone. The pendulum should start to rotate and then keep oscillating backwards and forwards. It is best to set the hands a minute or two in advance before the door is put back in so that the lever can be released at the correct time. If the clock was stopped abruptly or accidentally jarred, do not spin the pendulum round by hand as this can damage the suspension spring and the escapement mechanism. To start the clock again, gently move the pendulum in either direction by about half of a complete rotation (180°) using something like the eraser on the end of a pencil.