1. American National Standard Safety Requirements for Portable Metal Ladders;American National Standards Institute;ANSI A14.2–982,1982
2. Ladder climbing Biomechanics;Bloswick,1984
3. British Standard Specification for Portable Aluminium Ladders, Steps, Trestles and Lightweight Stagings;British Standard Institution,1984
4. DIN 4568 Teil 1–2;Deutsches Institut für Normung,1984
5. DIN 4568 Teil 1–2;Deutsches Institut für Normung,1984