Conversion of Time Range into Minutes

Date: 11/13/2002 at 17:24:03
From: David Bird
Subject: Conversion of time range into minutes

Hello,

I'm currently relieving a position that contains a quality improvement 
role. One report is related to utilisation of time, requiring me to 
report on 'time available' and 'actual time used' within operating 
theatres.
 
Let's say the "time available" is from 0830 (start) until 1600 
(finish), and the "time used" is 0835 - 1704.

What equation/conversion can I use to find the number of minutes 
between the start and end times for both 'available' and 'actual' time 
on a 24-hour clock?

Having an equation/conversion would save literally hours of currently 
manual calculations.

Regards,
David.

Date: 11/14/2002 at 23:10:36
From: Doctor Ian
Subject: Re: Conversion of time range into minutes

Hi David,

I'm not entirely sure I understand what you're asking. To avoid doing
the calculations 'manually', do you intend to program a computer or
spreadsheet to do the calculations? A spreadsheet like Excel or the
equivalent can subtract times directly.  

To subtract by hand, there are two cases. First, the number of minutes 
in the end time is greater than in the start time. In this case, you 
can just subtract the times as if they were integers:

    1744
  - 0835
  ------
     909

The second case is _not_ like this:

    1704
  - 0835
  ------
    ????

In this case, you can still do something like an integer subtraction,
instead of borrowing a 1 from the third column (which would represent
100 minutes), you borrow a 6 (which represents 60 minutes):
  
     6 6
     |
    17 04
  - 08 35
  -------
     8 29

     ^  ^
     |  |
     |  +------  this is (60+4) minus 35
     |
     +---------  this is (17-1) minus 8

That's really the only difference. If the interval spans midnight, you 
can borrow 24 hours,

    24
   
     1 6
     |
    02 04
  - 16 35
  -------
     9 29
     ^  ^
     |  |
     |  +------  this is (60+4) minus 35
     |
     +---------  this is (2-1+24) minus 16

Does this help?

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