If you use openoffice or libreoffice, here's how to set up when opening csv files. It will save them correctly afterwards as well.
Also make sure to set the formatting on the cells you are editing to number. Easiest fix is (if you want ALL the numbers to show up as numbers and not dates or something else) to click on the rectangle in the upper right of the cells (or ctrl+a, or edit->Select_Alll). Then you right-click and select "Format Cells..." (should be second entry), and make sure Number is selected in the right-most column, General in the second, and then click okay.
Also: notepad++, libreoffice, and Gimp are all awesome and free fyi
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