Converting from AM/PM to 24 hour clock:

between 12:00 AM and 12:59 AM, subtract 12 hours: 12:59 AM --> 0059 between 1:00 AM and 12:59 PM, a straight conversion: 10:00 AM --> 1000 between 1:00 PM and 11:59 PM, add 12 hours: 10:59 PM --> 2259

Converting from 24 hour clock to AM/PM:

between 0000 and 0059, add 12 hours: 0059 --> 12:59 AM between 0100 and 1159, straight conversion to AM: 0100 --> 1:00 AM between 1200 and 1259, straight conversion to PM: 1259 --> 12:59 PM between 1300 and 2359, subtract 12 hours: 1559 --> 3:59 PM

definition

Terms for using data resources. CD-ROM available. Credits and Acknowledgments for WW2010. Department of Atmospheric Sciences (DAS) at the University of Illinois at Urbana-Champaign.

am/pm to utc