IMPORTANT WARNING: The development of the GRACE webtool was completed in April 2008. Harmonisation with the IMPACT Handbook was then carried out and tests were conducted in May/June 2008. Additional tests are being carried out, that might lead to further adjustments and improvements. The developers will be grateful for any comment and suggestion from the users that might help fine tuning the tool. Please address your comments to Nicola Piccioni: npiccioni@isis-it.com