The Graph It plugin created by Rick Wilson with Smustard is a tool that allows you to enter functions of graphs to create graphs within your model. This is great for designing based off of specfic engineered dimensions, such as a design for a piston, where the curvature is crucial to the design. This plugin does have its drawbacks, when entering in the equation it is not obvious what each variable actually stands for and you do need to refer to his website for the explanation.
The xmin and xmax state the range of the function and the xinterval is the spacing. The variables follow this function:
y = a*x^q + b*x^r + c*x^s + d
This plugin is great, but it would be nice to have some more direction on the graph menu and possibly some more math functions. Maybe with the ability to automatically revolve the function and the ability to calculate area.
Overall, the Graph It plugin created by Rick Wilson is a great way to get your curves specific to what you want. At the time of this review this plugin is free and is available at Smustard.com. I give this plugin 3 out 5 stars.