VDI 4700 Blatt 3:2013-12

In national and European standards, a multitude of symbols are used, which have identical meanings but different notations. On the one hand, this is due to internationalisation in standardisation (e.g. DIN EN, DIN EN ISO), on the other hand, to technical rules being drafted by different bodies and the symbols being used in various branches of industry. This standard specifies the preferred usage of symbols in standards. Also symbols are preserved in spite of being outdated, because of their origin in the principles of thermodynamics.