Abstract: Apparatus for measuring the fluid characteristics of a sample comprises a frame, at least a first stage mounted on the frame for rectilinear movement, first mounting means mounted on the first stage, and a first member carried by the mounting means, a second member mounted to the frame in register with the first member, at least one of the first member and second member being readily interchangeable, positioning means for moving the first stage to adjust the relative positions of the members whereby a sample carried by one of the members can be brought into contact with the other of the members and whereby to adjust the spacing between the first and second members to a preselected distance, a device for vibrating the first mounting means rectilinearly, and thus the first member carried thereby, at a preselected frequency.