Thanks Ellie. I noticed because I was obsessing about the quantity for the whole 3 days - ie. I'd make a mental note of which printed letter on the cartidge that the plunger aligned with and then check that it had moved afterwards, just so I'd be doubly sure that the drug was actually passing through the needle! Plus I wasn't happy until I'd pulled the pen apart (not totally) and figured out exactly how everything worked. A bit OCD, I know...