For my idiophone, I chose The Ugandan Xylophone What Lives In The Gamelan Room. (Gotta be specific.) I counted the keys (there are 17), then measured the longest, the shortest, the widest, length of the frame, the height of the frame, the thickness of the wood, the thickness of the felt that the keys rest on, the height of the pegs that hold the keys in place. . . everything I could possibly think of to measure about this instrument. Then I looked up published measurements for Ugandan xylophones and discovered that all anyone really cares about is the number of keys. Which ranges officially, according to The New Grove Dictionary of Music and Musicians, from 6 to 22 keys. Sigh. I wrote that down on my homework and handed it in, along with all of my personal measurements.
The I.N.P.O.D. actually squealed when she saw it! Apparently, despite teaching this xylophone for years and years, she'd had no real idea of its dimensions before, and she was excited to see this wonderful little fact sheet about her very own instrument.
I felt like a million bucks for doing that. It was a good class.