Dictionary
Rock'well num"ber
Metall.
a numerical expression of the hardness of a metal as determined by a test
(Rock'well test") made by indenting a test piece with a Brale, or with a steel ball of specific diameter, under two successive loads and measuring the resulting permanent indentation.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.