Military Time, Decimal Time

Date: 08/05/2003 at 15:47:38
From: Kelly
Subject: Military time

For work we need to fill out our time cards in military time. I've 
heard of military time when referring to the 24-hour clock, but this 
job is different. I can never figure out my start and end time.  
Sometimes my out time is 28.9 or something weird like that. I don't 
understand how they get a number over 24 and how do they figure the 
.9 or .7, etc.?  I need a chart or something to refer to, but I 
can't find any info on this specific form of military time.  Help!

Date: 08/06/2003 at 12:12:48
From: Doctor Peterson
Subject: Re: Military time

Hi, Kelly.

What you are using is not military time, though many people confuse 
decimal time with military time because of the way they are written.

I have never heard of a way of reporting time that goes beyond 24 
hours; can you give me an example of the times involved when you get 
such a number? Does the whole part of the number generally agree with 
the number of hours, or not? Do you fill out your times based on some 
instructions you were given, or do you report hours and are told how 
long you worked in this system?

Apart from the 28.9 example, I could guess that you just use decimal 
hours, so that 30 minutes, which is half an hour, would be reported 
as 0.5. To convert minutes to decimal hours, you just divide the 
number of minutes by 60 (since a minute is 1/60 of an hour).

If you have any further questions or information, please write back.

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/ 

Date: 08/06/2003 at 14:31:24
From: Kelly
Subject: Military time

Yes, thank you.  I knew I wasn't crazy. When I said I was confused, 
my boss just looked at me and said "You don't know how to use 
military time?" She made me feel stupid. Anyway, for example, on 
Friday we reported to work at 2:00 pm and clocked out at 4:45 (or 
4:50) am.  I had to fill out my time card as arriving at 2.0 and 
leaving at 28.8.  What kind of system is this?

Date: 08/06/2003 at 15:01:53
From: Doctor Peterson
Subject: Re: Military time

Hi, Kelly.

Thanks. This is just what I needed. It helps to know that you work 
the night shift, crossing from one day to the next, which explains 
the 24 hour part. But I'm not sure about that starting time of 2.0; 
for a PM time, I think it should be 14.0. Please check that out for 
me; I'll assume I'm right for now.

Let's look at a timeline, starting at midnight beginning the day you 
came to work:

  Friday                                          Saturday
  AM                      PM                      AM
                      1 1 1                   1 1 1
  0 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6 7 8 9 0 1 2 1 2 3 4 5 6
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                              |============================|
                           2:00 PM        worked        4:50 AM
  |<------------------------->|
       start: 12+2=14 hours
  |<------------------------------------------------------>|
                       end: 24+4.8=28.8 hours

  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0

Both times have to be measured from the same point, though they are 
in different days, so that they can be subtracted to find the elapsed 
time. So the starting time of 2:00 PM is seen as 14:00 (as in genuine 
military time), and converted to decimal as 14.0. The ending time is 
4 hours and 50 minutes, or 4.8 hours (since 50/60 = 0.83 hour) after 
the start of Saturday, and 24+4.8 hours past the start of Friday. 
That's why you use 28.8.

It would be funny if your boss told you to use 2.0 for the starting 
time, because calling it 14 is the one part of this scheme that IS 
military time (and using 2.0 would give you credit for 12 extra hours 
worked).

Let's break this apart. There are three aspects to the time system 
you are using:

1. It is military time in that you don't use AM and PM, but count 
from 0 up to 24.

2. It is decimal time in that you don't report minutes, but tenths of 
an hour (every 6 minutes is a tenth of an hour).

3. The time you leave is counted relative to the day on which you 
started work, so that times on the following day are counted as 24 or 
more, rather than starting back at zero.

That's enough to confuse anyone who hasn't had it all explained 
clearly!

- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/ 

Date: 08/06/2003 at 15:29:46
From: Kelly
Subject: Thank you (Military time)

Thank you for all your help. I work weird hours (TV production) so I 
don't always work nights. No matter when I start they have me use the 
exact number of the time I start (ex. - 10:00 am would be 10.0 or 4:00 
pm would be 4.0). I thought that seemed weird, but at least I now know 
I'm not the only one. Thanks for clarifying the minutes (every six 
minutes is a tenth). That helps as well. Thank you!