I keep playing around with this in my head and I can’t come to anything but the conclusion that the unit of analysis for a sequence in interaction design is always dependent on the interaction and that dependency is because something is inherently important about each artifact and their functions differ.  Or maybe it’s based on function?  Can two artifacts that do the same thing have the same unit of measure in a sequence analysis?  Or is it based on the sequence chosen that the unit of analysis?  Would it be better to set the units of measure before even considering an artifact or would that miss the point?