"The Merg" wrote in message
...
I am working on a timesheet in Excel and seem to have come upon a strange
quirk/error. The timesheet is supposed to take two times, find the
difference
and then display it in decimal format.

For example:
A1 = 09:00
A2 = 09:30
A3 = 0.5

The formula I have in cell A3 for making this computation is:

ROUNDUP((A2-A1)*1440/60,1)

The idea of the roundup is so that as soon as you work more than a
specific
tenth of an hour you get credit for the next tenth. The breakdown of an
hour
would be as follows:

.1 = 1-6 minutes
.2 = 7-12
.3 = 13-18
.4 = 19-24
.5 = 25-30
.6 = 31-36
.7 = 37-42
.8 = 43-48
.9 = 49-54
1.0 = 55-60

The issue I am having occurs for time differences of 30 minutes but only
at
specific times. One of these ranges for example is 14:30 to 15:00. When
the
formula calculates the time difference it comes out incorrectly to just
over
.5 so it is rounded up to .6.

Does anyone have any ideas on how to workaround this or why Excel does
this?

This is likely to be yet another example of where calculations involving
decimal numbers gives ansswers which don't come out quite right. You need
to remember that Excel times are stored as fractions of a day, so 06:00 will
be 0.25, and secondly you need to remember that Excel works in a binary
representation, so while it can represent numbers such as 0.5, 0.25, 0.125,
0.375, etc. it can't give an exact representation of numbers like 0.1.
Excel works to 15 significant figures, but there will be small inaccuracies.

Your 30 minutes is 0.20833333... of a day, so can't even be represented
accurately in decimal, never mind in binary.
--
David Biddulph