Simplify the following text for a Grade 7 native English-speaking person.
Original: The 24-hour clock is a convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours , indicated by the hours passed since midnight , from 0 to 23 .
Simplified: The 24-hour clock is a way of telling the time in which the day runs from midnight to midnight and is divided into 24 hours , numbered from 0 to 24 .