A rectangular bar will produce different pitches depending on whether it’s struck from above or from the side, due to being thicker across one dimension than the other. With an angle strike along the edge it will produce more than one pitch. For each of these directions of vibration the bar has additional 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. Several sets of bars are included in the instrument, each set with a different multi-mode tuning of its bars. For details, see here.