Gerd Kaupp (2022) “Significant Effects of the Exponent 3/2 for Pyramidal and Conical Indentations: New Meanings of Physical Hardness and Modulus”, Basic Mathematics for Physically Correct Mechanical Properties from Indentations, pp. 8–22. doi: 10.9734/bpi/mono/978-93-5547-921-1/CH2.