How to select data for a chart, from another workbook?

I've created a chart that uses dates and figures from another worksheet in the same excel file.
The problem is that while this works fine, I run into problems in that I have dates for one year in each worksheet and then their will be twelve charts, each in their own worksheet. This makes the workbook too cluttered and difficult to navigate. So I wanted to have the worksheets with the dates in them in a separate workbook, and the charts in another workbook.
How do I reference the values in another workbook when selecting the data for the charts?