Percussion bars like those in xylophones are normally laid out flat and struck from above, causing them to vibrate in an up-and-down direction. If you were to strike a bar from the side instead, you’d find that it produces a higher pitch because, being thicker across that dimension, it is more rigid for vibrations in the side-to-side direction. In other words, a rectangular bar will produce different pitches depending on striking direction, and with in-between strikes it will produce more than one pitch. The situation is further complicated by the fact that for each direction of vibration the bar actually has its own overtone frequencies as well. In the instrument shown here, each rectangular aluminum bar is tuned for multiple modes in both orientations, each bar thus producing a deliberately tuned chord-like cluster of pitches. Various tunings of the relationships between the tones within each bar are possible. Several sets of bars are included in the instrument, each set with a different multi-mode of its bars. For details, see here.