In parameterized mechanism design, there are two contradicting requirements: keep the governing equation as general as possible (everything in symbolic form), but be able to quickly look at (or simulate) the mechanism and see how it moves at every stage of the design process (which requires numeric representation). Handling symbolic and numerical representations together is a basic paradigm of symbolic manipulator programs like Mathematica. The solutions developed for this paradigm can be used for enhancing the flexibility of a mechanism prototyping application package written in Mathematica. This article shows some examples of mechanism modeling with the LinkageDesigner application package that uses this bundled symbolic and numeric representation. The bridge between the two representations is substitution, enabling a one-way route from symbolic to numeric representation. A historical parabola-drawing mechanism and the spirograph will be used as examples. Besides the power of substitution, replacement is also widely used in LinkageDesigner. This simple tool can be handy in solving problems like the inverse kinematic problem (IKP). Two examples will be considered: the IKP of a 6R robot and a parallel mechanism with three degrees of freedom.