Four-barlinkages are used to convert a uniform continuous rotation into a non-uniformrotation or oscillation. The apparatus has a disc with angular scale which isused to measure the exact input angle. The crank pin can be located atdifferent radii on the disc. The four-joint link is a four-bar pivot gear.It converts rotary motion into oscillating motion. The unit can be used toinvestigate the crank-rocker mechanism, the double rocker mechanism andthe double crank. The experimental unit comprises the drive disk with thecrank and coupling and the output disk with the rocker. The elements areconnected to each other via pivot joints. The positions of the pivotjoints can be varied to adjust the crank radius, oscillation radius andcoupling length. The drive disk can be driven by the crank. The inputangle is adjusted using the drive disk, and an angle scale is integrated intothe base plate. The output angle is read at the angle scale on the outputdisk. The elements are mounted on a base plate. Two handles make it easyto carry and stack the unit.