David Henshaw Whittemore (1832-1892) designed The Union Apple Parer to pare in the forward and reverse directions (Whittemore, 1866). The drive and intermediate gears have a series of cams along their inside. The drive gear has 4 cams that turn the intermediate gear. The intermediate gear has 10 cams that are so arranged as to rotate the paring knife segment gear clockwise to pare an apple from stem to calyx and then counterclockwise to pare a second apple from calyx to stem. I like to think of these cams as modified helical gear teeth.
The Union Apple Parer was a very successful design that evolved over time, see our evolution section. Videos showing this apple paring can be found in this section under Union with Push-Off.