One of the difficulties of the CDM is in judging whether or not projects truly make additional savings in GHG emissions (Carbon Trust, 2009, p. 54-56). The baseline which is used in making this comparison is not observable. According to the Carbon Trust (2009), some projects have been clearly additional: the fitting of equipment to remove HFCs and N2O. Some low-carbon electricity supply projects were also thought to have displaced coal-powered generation. Carbon Trust (2009) reviewed some approved projects. In their view, some of these projects had debatable points in their additionality assessments. They compared establishing additionality to the balance of evidence in a legal system. Certainty in additionality is rare, and the higher the proof of additionality, the greater the risk of rejecting good projects to reduce emissions.