-0:00:05
-0:00:10
0:00:03
=sum(A1:A3)

=date(left(A1,4),mid(A1,5,2),right(A1,2)
Where A1 is the cell containing the date.

The new cell will contain an excel date value for that day,
right click the new cell, and select the date format you want.

Couse CQ15 is a text cell. For calculate with it, you must format it as time value.
=IF(LEFT(CQ15,1)="-", -TIMEVALUE(RIGHT(CQ15,LEN(CQ15)-1)), TIMEVALUE(CQ15))

[quote]I am trying to calculate a negative formula for shift time not fully worked. Say data is as follows: A1 = 07:30 shift start, minus A2 = 1:00 lunch break A3 = 16:30 shift ends Then A4 = 8:00 hours worked during the day. But, should the worker leave earlier, say 17:00, what is the formula in cell A5 that shows how much short the person's shift was?By Meg[/quote] You can't directly display a negative time in Excel. However, you can display it using the TEXT() function. For example Cell A4 would have =A3-A1-A2 which will display the hours/minutes worked. Cell A5 would have 8:00 which is the number of hours you expect this person to work Cell A6 would have =IF(A5=A4,"Met expected target",IF(A4

[quote]If you switch to 1904 all dates in the workbook change. Not a solution. What is this 1904 thing anyway?By Ralf[/quote] The 1904 format comes from Excel version 1.0 which was on the Macintosh. Two years later Microsoft released Excel for Windows and with with that release introduced the "1900" date format. Excel for the Mac continued to default to the 1904 format and Windows defaults to the 1900 format. Both versions can switch to the other format but doing so will cause all dates in a workbook to shift. The year 1900 was special in that though it's divisible by 4 it was not a leap year. The Mac's clock hardware did not have the extra logic needed to handle this special case and so Apple simplified the design by allowing for dates from 1904 (the first leap year in the century) on out. As Excel was first written for the Mac it was natural that Excel would use the Mac's date format. The developers of Excel for Windows used the 1900 format for backwards compatibility with SuperCalc and Lotus 1-2-3 which were the dominate spreadsheet applications in the MS-DOS and Windows markets at the time. The 1904 and 1900 formats are nearly identical. The 1904 format stores dates as the number of days since 1/1/1904 and the 1900 format is the number of days since 1/1/1900. You can convert a 1904 date to a 1900 date by adding 1,462 to a cell's value and subtracting 1,462 to convert the other way. Apparently the developers of Excel for the Mac included code to support negative time values. The coders of Excel for Windows did not support negative time values. Modern versions of Excel still include two separate chunks of code with one dealing with 1904 dates and the other for 1900 dates. They never fixed the 1900 code to support display of negative time values.

Thanks for the history lesson, Marc. Much clearer now how it came to this. Still leaves me wondering about your last sentence: "They never fixed ..." I don't get it. Would it be so hard to fix? So I still need to use Libre Office for two things: negative times and CSV export. Must be exotic niche features ...

Couldn't you just multiply the numbers by -1 to start, add them up then multiply by -1 again?