In synthesizing a planar 4R linkage that can achieve four positions, the fixed pivots are constrained to lie on a center-point curve. It is widely known that the curve can be parametrized by a 4R compatibility linkage. In this paper, a slider-crank is presented as a suitable compatibility linkage to generate the center-point curve. Furthermore, the center-point curve can be parametrized by the crank angle of a slider-crank linkage. It is observed that the center-point curve is dependent on the classification of the slider-crank. Lastly, a direct method to calculate the focus of the center-point curve is revealed.