A process for manufacture of a component made of opaque synthetic quartz glass, and a quartz glass tube manufactured according to said process. Each subset includes all but the most significant bit of a corresponding row address. A tool has an interior passage of a size that can receive a target whereby a physical therapy patient can grasp the tool and place the tool on a target designated by a therapist such that the target is located in the interior passage of the tool. If a block is not textured, the tool further classifies the block as dark smooth or smooth depending on average intensity value for the block.