1. Tabor, D.: The hardness of Metals, Oxford C. Press, New York 1951
2. O'Neill, H.: Hardness Measurement of Metals and Alloys, Chapman Hall, London 1967
3. Maxwell, B.: Mod. Plast., 32, 125, 1955
4. Baer, E., Maier, R. E., Peterson, R. N.: SPE J., 17, 1203, 1961
5. Racke, H. H., Fett, T.: Materialprüfung, 13, 37, 1971