You want to save an Excel tab as a csv file with Excel 2010 but you do not want to lose any precision of numbers?
Then let us have a look into this:
Excel 2010 and older versions suffer from the disease of losing precision of numbers when exporting a tab as a csv file. Excel only saves the displayed significant digits for numbers, not the internally stored precision.
Example: Create a new spreadsheet. Enter 123456789012345 into A1. Save this as a csv file. Close the file. Then open it again. Now A1 only contains 123457000000000..
How can you avoid this?
Before saving as csv, select all cells of your tab (select upper left cell left of column A and top of row 1, go to number format, then select scientific format with 15 digits of precision. There you are: