The m/z delta values are always expressed as measured minus computed, with default units as m/z and deltas in parts per million listed with a suffix of 'ppm'. Finally, the confidence of one or more annotations may be specified with a '*' followed by a number between 0 and 1, inclusive (e.g. *0.97). It may be used to indicate the relative confidence between alternative explanations or to indicate a confidence that a proposed explanation is truly the source of measured peak (perhaps based on a model of the m/z deltas for the spectrum and likelihood that such a fragment ion would be present).