Claim: The 12-hour clock divides the 24 hours of the day into a.m and p.m.

The 12-hour clock is a time convention in which the 24 hours of the day are divided into two periods : a.m. -LRB- from the Latin , ante meridiem , meaning before midday -RRB- and p.m. -LRB- post meridiem , meaning past midday -RRB- . Each period consists of 12 hours numbered : 12 -LRB- acting as zero -RRB- , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , and 11 . The 24 hour/day cycle starts at 12 midnight -LRB- often indicated as 12 a.m. -RRB- , runs through 12 noon -LRB- often indicated as 12 p.m. -RRB- , and continues to the midnight at the end of the day .   The 12-hour clock was developed over time from the mid-second millennium BC to the 16th century AD .