What version of Excel (2007 or earlier)?
The problem is just with one file or any file that you make a chart?
When you 'change the ranges', what actions do you perform?
What you are observing is very odd

--
Bernard Liengme
Microsoft Excel MVP
http://people.stfx.ca/bliengme

"Bill Ridgeway" wrote in message
...
Every time I change the x and y ranges on ANY line graph generated from an
excel file the date format on ALL open files and ALL files opened
subsequently is changed from dd/mm/yyyy to dd/mm/yy. Although this is not
a permanent change (the format is correct on re-starting Excel) it is
annoying. Can anyone please suggest why this is happening and if it can
be remedied?

Thanks.

Bill Ridgeway