Bassist and Pianist, ink and pencil drawing, A4 sketchbook
Here's a video of some of the performance from Youtube, which unwittingly features the back of my head. Besides seeing what I was working from, careful observers might spot which bits I was looking at when, and when I finished the drawing and started adding tone.
It goes without saying I'm the guy in the suit, not the lady who's also drawing. (Turns out she'd been to a conference during the day in the building and happened to sit next to me.)