Most think that all every day clocks are 24 hours clocks because they are mentally conditioned to work out the difference between a.m. and p.m. thereby confusing themselves with a 12 hour clock which actually rotates twice in 24 hours.
A 24 hour clock rotates only once per day. For that reason some find them difficult or slower to read, but actually prefer to see at a glance the difference between 3 a.m. and 3 p.m. as it would read 15 hours. Americans refer to a 24 hour clock as a Military Clock.
For some it is only the hour is important at a glance, so for a speedier reading of the clock we have a single indicator hand version indicating the hour, but it is still easy to devide the hours visually to see when it is quarter past or half past the hour.