IEC 61966-2-1 does not use the term gamma or effective gamma, instead defining the term "display input/output characteristic" and "encoding characteristics". The IEC justifies this in Annex A, a non-normative section labeled as "informative." Annex A starts with a brief history of the term gamma, and then several unreferenced and unsupported claims that the term is somehow ambiguous, and finally an ultimatum that the term is detrimental and that the IEC chose not to use it. This despite its common understanding, and use in industry and other standards documents. As a result, throughout the 61966-2-1 document, instead of the term gamma, the IEC uses terms such as ""display output characteristic"" or ""simple power function"" or ""normalised output luminance as represented by an exponential function"."