Hope this is the right forum, I'm using Excel 2007 in VirtualBox on a Macbook Early 2006. When I autofill a date/time in column A: 1: 1/1/2009 0:00:00 2: 1/1/2009 1:00:00 etc... I find that after about 5 days, ie 5/1/2009, the time starts to drift, only by a second, but progressively gets worse over time. looks like this 5/1/2009 4:00:01 or even 5/1/2009 3:59:59 10/1/2009 4:00:02 and so on... My question is why does this happen (is it related to accuracy in excel) and is there some way to fix it? This concerns me because I'm working with a large datasets that need to be merged with another dataset for statistical analysis and the merge doesn't work if the date/time match is not exact. I've tested the autofill in openoffice and initial tests don't seem to have this problem. I know I could use openoffice, but at the moment a quick fix in excel would be preferable.