DIN SPEC 91020 [Withdrawn] references following documents:

Document number Edition Title
DIN EN ISO 10075-3 2004-12 Ergonomic principles related to mental workload - Part 3: Principles and requirements concerning methods for measuring and assessing mental workload (ISO 10075-3:2004); German version EN ISO 10075-3:2004 More 
DIN EN ISO 26800 2011-11 Ergonomics - General approach, principles and concepts (ISO 26800:2011); German version EN ISO 26800:2011 More