Same as above but unit is electrically operated to give the following 12 rates or strains. 1.25, 0.625, 0.25, 0.125, 0.05, 0.025, 0.01, 0.005, 0.002, 0.001, 0.0004 and 0.0002 mm/min. The apparatus is suitable for operation on 230 volts single phase A.C. Supply.