After rockfall damage with adhesive tape so that no dirt enters the disc. Then follow the instructions. It worked the first time quite well and the rock falls in my disc can not be found again. The second time I had a major falling rocks, about 2 mm. After the application of rock fall was no longer visible, but it was a tear in the disc, about 1.5 cm long. This could not be removed by reapplying.
Conclusion: If possible let make a professional. Otherwise, think of the risk to worsen the damage and know how expensive a new windscreen is.