A bathtub rim assembly is disclosed that includes a support structure that is capable of engaging a rim of a bathtub to prevent substantial deformation and damage to a cantilevered ledge of the bathtub. The mixture is introduced tangentially into a cooling jacket. Thus, the measuring area per unit time is reduced effectively. In addition, by having the air flow along the annular recess, which is formed with a substantially trapezoidal shape in cross section, the workpiece is maintained in a non-contact state with respect to a holding surface of the inner member. A second resistor is connected at one end to a source of the NFET and a drain of the PFET, and connected an opposite end to another line of the differential transmission line.