I am informed by a flying instructor at my local flying school that the reason for requiring the student to call undercarriage down and locked on a fixed gear aircraft, is that one day the pilot might fly a retractable and therefore is a GOOD THING to get used to.
I see. Then in that case should not the student call "undercarriage up and Locked" in a fixed gear aircraft for the after take off checklist - just to be consistent? Funnily enough I have never heard that used
Sorry to burst your bubble their Centaurus, but our flying school and another that I know of actually get their students to Call '200ft', Flaps Up, Gear Up and locked, check track.!
T&G