The board, built by tinkerer John Sarik, has two knobs for selecting the correct square and a keypad for punching in numbers.
And while we're at it - things harder than making a nixie tube Sudoku board? The card game bridge. But if somehow you do know how to play bridge and are up for the (lesser) challenge, Sarik as the full schematics for the build on his site. [TrashBear Labs via HackaDay via Make]