The laser should be mounted so that the light from it follows the line marked on the arm to which it is attached. In practice this means that provision needs to be made for adjusting the position and orientation of the laser module on the rotating arm which can be achieved by inserting the laser capsule into a block of aluminium with a hole of appropriate diameter bored along its length. As illustrated in figure 2, the position and orientation of the capsule can then be adjusted by means of transverse clamping screws. It is helpful to reduce the diameter of the emerging beam of light by passing it through a hole of diameter 1 mm drilled in a piece of shim brass glued to the end of the aluminium block.