The program is a graphical tool to visualize 4-bar mechanisms and the instant centers that are produced by the mechanisms, and plots the path of the instant centers.
The paths (polodes) of the instant centers are shown for the mechanism and the inversion of the mechanism (switching the coupler link and the ground).
The polodes represent two curves, that when one roles on the other, produces the same motion as the original 4-bar coupler that made them, e.g. the 4-bar can be synthesized by a 2-bar mechanism consisting of only the fixed and moving polode. The moving polode curve will have two points on it that travel in circles, just as the original coupler did on the 4-bar.
You can select from 15 different types of 4-bars, e.g. cranks and rockers or combinations of the two.
Also, you can specify any link length of interest, numerically or with slider bars, and do so while the animation is running (but hit the "change links" button.)
There is a slider bar to adjust animation speed and input angle specification. If you "stop" the animation, the input angle may be specified by dragging the slider to move the mechanism.
If you just want to see the 4-bar animate, uncheck all the boxes under "Display"
Lastly, two zoom options are provided.
Feedback for improvement or other ideas is welcome.