You can set Excel 2010 to create a backup copy of the workbook every time you save. This is stored in the same folder and named Backup of (your filename).xlk. Like Word’s backup copies, it is a copy of the version you last saved.
You set this through the Save As dialogue.
Go to File>Save As
Choose General Options from the Tools menu at the bottom right of the Save As window.
Then tick Always create backup
This setting will then apply to this particular workbook. You will have a current version and one previous version saved in the same folder.
If you want it to be the default for all new spreadsheets, you need to apply this setting to the file called book.xltx which is located in your XLSTART folder. That folder is usually located here C:\Users\username\AppData\Roaming\Microsoft\Excel\XLSTART