A laser is then fixed to the spindle and directed to the nadir. The laser does not have to be in line with the spindle for this test, it can be to one side. When the spindle is rotated, the spot should remain stationary. If it does not it will describe an ellipse, which will be very nearly a circle. The centre of this should be marked and the laser directed towards it (Figure 13(b)). The spot should remain stationary. The distance between the nadir found with the plumb bob and this spot indicates the amount that the spindle is out of vertical. An adjustment should be made accordingly.