Spuds...
Here at TC, we quite often get our bretheren from across the pond replying to a call of climb FL130 with "climb 0ne three thousand"... etc etc
if you were to say "climb to 4000 feet"; would they maybe take that as clearance to climb to FL240??
I know it should be obvious, but when you normally fly in a country with a transition altitude 2 or 3 times higher than in the UK, I suppose it can be confusing. (Can't believe I typed something that could infer a defence of the Yankee pilots!!)
Beaten to the punch by Gonzo....