Abstract: An apparatus and method for measuring the flow stress and like characteristics of metals and other material especially at hot working temperatures. The specimen is struck simultaneously by projectiles of equal mass but unequal velocity. The velocities of the projectiles and the dimensions of the different indentations produced upon the specimen by the projectiles are terms in the formula by which the flow stress is calculated. A formula requiring only two projectiles is adequate for many materials; one requiring three projectiles may be better for materials that show work-hardening when they undergo strain at high temperature. The projectiles may be propelled pneumatically or by contact with a driven lever. Alternatively the projectiles may be in the form of masses carried as pendulums.