This is said with confidence, but it’s wrong. As a note on this note for Americans, Professor in America is also the senior non-managerial rank. Professor rankings in order: Assistant Professor, Associate Professor, & finally Professor. And if you do it long enough you may get Emeritus status!
BeijingPalmerjust as a note for Americans on the whole very sad Arday affair (he just resigned), becoming a 'professor' at Cambridge is a bigger deal than at a US institution. 'Professor' is the senior non-managerial academic rank in the UK; what would be 'professors' at US institutions are 'lecturers' in UK.