Abstract: An assembly that provides for the mounting of paired sets of lubricant sample holders into balanced, opposed contact with a rotating rotor and whereby comparative data pertaining to measured load, speed and elicited thermal, audio and visual responses are obtained. The coded data is stored for digital comparison. In one assembly, a metal disc is mounted to rotate from a motor drive shaft in a cylinder block and in contact with calibrated sample support bushings biased to contact upper and lower surfaces of the disc. In another construction, an annular cylinder block supports several radially directed, opposed pairs of sample support bushings in biased, tangential contact with a circumferential wall of a cylindrical race or spherical rotor. Pneumatic or hydraulic pressure may be used to augment or load each bushing. In yet another construction, an annular cylinder block supports a pair of opposed weighted lever arms and sample support bushings in tangential contact with a rotor surface.