Hewlett Packard 54600 series Oscilloscope (included game)

The Hewlett Packard 54600 series Oscilloscopes includes a game as an Easter egg or at least undocumented feature. The game is summoned when pressing the second and third softkeys simultaneously.

The game is a variant of Tetris. Pentomino blocks appear at the top of the screen and drop down towards the bottom. The player can move the blocks left and right and rotate them as they fall down. The blocks stack but whenever a full line of the play area is filled the line is removed, freeing up space and scoring points. The game is over once the spawned piece no longer fits in the play area. The game features multiple difficulty levels.