There is another way, but frankly it's hardly worth the effort: use the
properties of the "named range" facility in Excel (that should really be
called "named function", as range is only part of what it can do) to
refer to the original data range and divide its values by a thousand.

There are all sorts of pitfalls and ways to mess it up: I just spent a
few minutes trying to get it to work. It's really better to just go with
the helper range, then at least people trying to work with your
spreadsheet will be able to understand what you did.

Named ranges can be very powerful tools for some charting applications
(see

http://peltiertech.com/Excel/Charts/DynamicColumnChart1.html

for an example), but they're too fiddly to be bothered with for
something as simple as this.