Sometimes this happens when the chart is in a different workbook from
the data. If the source workbook is not open, Excel doesn't read the
format that was applied to the data, so it just applied General number
format. The way to minimize reformatting is to double click the axis
before it messes up, go to the Number tab, and uncheck the Link to
Source checkbox. This makes the chart remember the format, not get it
from the source data.

- Jon
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Jon Peltier, Microsoft Excel MVP
Peltier Technical Services
Tutorials and Custom Solutions
http://PeltierTech.com/
_______


Bernard Liengme wrote:

Not sure why it changes but it is not arbitrary. Excel stores dates a serial
number (1/1/1900 at midnight =0). Try this: enter todya's date in a cell and
then format it Number and you will see 38609.
Somehow your chart axis is getting reformamted.
best wishes