Practical and familiar knowledge of the principles and processes of an art, science, or trade, combined with tbe ability to apply them in practice in a proper and approved manner and with readiness and dexterity. See Dole v. Johnson, 50 N. II. 454; Akridge v. Noble, 114 Ga. 940, 41 S. E. 78; Graham v. Gautier, 21 Tex. 119; Ilaworth v. Severs Mfg. Co., 87 Iowa, 765, 51 N. W. 68.