to an outer housing apparatus of this type is generally referred to as u201c point the bit u201d types since the axis of rotation of the bit is changed from the axis of rotation of the driving drill string an outer cylindrical housing 20 contains two eccentric cylinders the outer eccentric cylinder 21 and the inner eccentric cylinder 22 interior to the inner eccentric cylinder 22 is the drill string pipe 23 the center of the outer cylindrical housing is at 24 in the left hand cross section a the eccentric cylinders 21 and 22 are positioned with their eccentricities opposite each other so that the drill string pipe 23 is centered on the center of the outer cylindrical housing at 24 in the center cross section b the eccentricities of the eccentric cylinders are aligned and the drill string pipe 23 is displaced as shown below the center of the outer housing at 24 this orientation of the offset may be rotated around the borehole axis to cause deflection in any desired direction further as shown in the right hand cross section c the magnitude and direction of the offset may be set to any desired magnitude and direction by combination of the angular positions of the two eccentric cylinders fig2 a adapted from u s pat no 5 803 185 shows another type of apparatus that is generally referred to as a u201c side force u201d type since a side force is generated just above the bit to force the bit in the desired direction the axis of.