The property of being abstruse; abstrusity.
The resistance to scratching, cutting, indentation or abrasion of a metal or other solid material.
The quality of being hard.
An instance of this quality; hardship.
The penetrating ability of electromagnetic radiation, such as x-rays; generally, the shorter the wavelength, the harder and more penetrating the radiation.
The measure of resistance to damage of a facility, equipment, installation, or telecommunications infrastructure when subjected to attack.
A measure of how hard a material is
The quantity of calcium carbonate dissolved in water, usually expressed in parts per million (ppm).