The Primer’s nanomolecular microscope helps Nell dip her toes into cellular biology, but it’s also a tool which makes expert biologists much more capable. It’s not a toy representation, a cognitive dead end which Nell must discard as soon as she builds an intuition. It’s a tool which can grow with her into legitimate practice, a tool which in fact expands the frontiers of practice for the entire field. My collaborator Michael Nielsen has long argued that this is true of all our most powerful representations.