24 hr clock is one that I never use, not that it is confusing, it is very confusing! Sometimes, you get mixed up by the time and you minus 10 hrs of the 24 hrs clock instead of 12, leading to some real embarassing events.

Anyway, I really like to use the metric system instead of the the inches system, we are supposed to use metric over here anyway. It is easy to me, from km to meters, times 1000. From meters to cm, times 100. It is real easy to remember. From feet to inches, you have to times 12. From miles to inches, I'm not even sure! HAHA, but once people are used to any system, they'll find it easy.