Assessment implies both something to measure anda methodof measuring it. One major barrier to sustainability assessment is the lack of an acceptable analysis method, as mentioned in the discussion of the holistic approach. This difficulty in data analysis may justify the introduction of a reductionist approach that advocates quantitative data in the assessment. As a most vital element, the degree of progress towards sustainability is unlikely to be recognised without numerical sources, as in economic development forecasting. For example, without any standards in the numerical sources, how is it possible to see the extent to which a tourist destination is getting better or worse, even if the destination should move from one qualitative category to another? Furthermore, as far as system quality is concerned, it could be difficult to define and explain the gradations (sectors of scale) of sustainability without the provision of quantitative data. Numerically based assessments have certain advantages, and such a system is proposed here.